Praise be to Allaah.
It is not permitted for the Muslim who believes in Allaah as his Lord, Islam as his religion, Muhammad (peace and blessings of Allaah be upon him) as a Prophet and Messenger, and in the divine decree, both good and bad, to think that any being, entity or quality can have a specific effect in bringing good or warding off harm, as there is no evidence in shareeah to that effect. This is part of the legacy of jaahiliyyah (ignorance) which has been cancelled out by Islam and is regarded as being shirk which negates perfect Tawheed, because it is insinuating thoughts (waswaas) and scare tactics from the Shaytaan.
It is like the attitude of the people of Pharaoh, about whom Allaah said (interpretation of the meaning): But whenever good came to them, they said, Ours is this. And if evil afflicted them, they ascribed it to evil omens connected with Moosa and those with him [al-Araaf 7:131]. If some disaster or drought befell them, they blamed it on evil omens which they associated with Moosa and the believers with him, but Allaah refuted this and said (interpretation of the meaning): Verily, their evil omens are with Allaah [al-Araaf 7:131].
Ibn Abbaas (may Allaah be pleased with them both) said: Their evil omens means what He decreed for them; they were the cause of what happened to them because of their kufr and rejection of the signs and messengers of Allaah.
Many ahaadeeth were reported from the Prophet (peace and blessings of Allaah be upon him) in which he forbade pessimism and superstitious belief in evil omens. The word tatayyur (pessimism) is derived from teer (birds), because some birds were viewed as evil omens, then the word came to be applied to everything that is taken as a bad sign. Abu Hurayrah reported that the Prophet (peace and blessings of Allaah be upon him) said, No adwaa[transmission of infectious diease without the permission of Allaah], no tiyarah [superstitious belief in bird omens], no haamah [refers to a Jaahili Arab tradition described variously as: a worm that infests the grave of a murder victim until he is avenged; an owl; or the bones of a dead person turned into a bird that could fly], and no Safar [the month of Safar was regarded as unlucky in the Jaahiliyyah]. [Translators notes in square brackets]. (Reported by al-Bukhaari, 5757, and Muslim, 2220.] Muslim added in one of his reports: And no naw (star promising rain) and no ghool (evil demon living in the desert).
The Prophet (peace and blessings of Allaah be upon him) denounced adwaa, the Jaahili belief that attributed sickness to something other than Allaah and said that the sickness could transmit itself without the decree of Allaah. He explained that all of that happens by the decree of Allaah, and that people are instructed to avoid the causes of disaster if they are in good health.
The words no Safar, according to one of the interpretations given by the scholars, refer to the month of Safar, which the people of the Jaahiliyyah viewed with pessimism as being unlucky, as was reported in Sunan Abi Dawood (3914) from Muhammad ibn Raashid from someone who heard him say: The people of the Jaahiliyyah used to regard Safar as inauspicious, and said that it was an unlucky month. The Prophet (peace and blessings of Allaah be upon him) refuted that.
Imaam Ibn Rajab (may Allaah have mercy on him) said: Regarding Safar as inauspicious is a kind of superstition that is forbidden. Also forbidden is regarding particular days, such as Wednesdays, as inauspicious, or following the Jaahili custom of regarding Shawwaal as inauspicious for weddings.
No doubt this also includes the superstitions about the number 13 mentioned in the question. There is no indication in the Quraan or Sunnah that this number should be regarded as inauspicious in any way. The thirteenth is just an ordinary day, like any other day, and anything that happens on such a day happens by divine decree; Allaah decreed that it should happen on that day in that way. If a person tried to spend his time counting the numbers of days or dates on which calamities befell the Muslim ummah, he might find some patterns in some instances, but this has nothing to do with bad luck because of certain numbers or dates on which those events happened.
The remedy for this kind of waswaas is for a person to strengthen his heart, have certain faith (yaqeen) in Allaah and put his trust in Him. He should know that no disaster happens except by the decree of Allaah, and he should beware of getting carried away with this waswaas from the Shaytaan or these ideas that may cross his mind. He may be punished with the very thing that he is fearing, because he is turning away from having faith in Allaah and the belief that all good is in His hands, and that He Alone is the one who wards off harm by His power and grace.
The Prophet (peace and blessings of Allaah be upon him) taught us the kafaarah (expiation) to be offered by the one who indulges in any kind of superstitious pessimism. Abd-Allaah ibn Amr reported that the Prophet (peace and blessings of Allaah be upon him) said: Whoever lets tiyarah (superstition) stop him from doing something is guilty of shirk. They said, What is the kafaarah (expiation) for that? He said, To say: Allaahumma la khayra illaa khayruka wa laa tayra illaa tayruka wa laa ilaaha ghayruka (O Allaah, there is no good except Your good, no birds except Yours, and there is no god beside You). And Allaah knows best.
As this issue is widespread among people nowadays, there is no harm in going into further detail, as follows:
In the Name of Allaah, Most Gracious, Most Merciful
Tiyarah and Fal (Bad omens and good omens)
 Tiyarah (seeing bad omens) comes from the word tayr (birds) [because the ancient Arabs used to see omens in the movements of birds and other creatures Translator], and is the opposite of fal (good omens). The Arabs all used to have the same ideas about fal and tiyarah. The Prophet (peace and blessings of Allaah be upon him) approved of and encouraged the idea of seeing good omens, but he disapproved and forbade the idea of seeing bad omens.
 Al-Izz ibn Abd al-Salaam said: The difference between al-tiyarah and al-tatayyur is that tatayyur means feeling in one's heart that something bad is going to happen, whilst tiyarah means acting on the basis of those pessimistic feelings.
 Tiyarah existed long before Islam. Allaah says (interpretation of the meaning): But whenever good came to them, they said, Ours is this. And if evil afflicted them, they ascribed it to evil omens connected with Moosa and those with him [al-Araaf 7:131].
 Types of superstitious belief in bad omens, ancient and modern:
Certain days or months, such as Safar and Shawwaal.
Certain birds, such as crows and owls.
Certain animals, such as snakes, black cats and monkeys, or their movements, such as the passing of gazelles.
Certain types of people, such as a one-eyed man or a hunchback.
Certain numbers, such as 13 among the Christians, 7 among the Bedouin and 10 among the Raafidis; in the latter case because they dislike the asharah mubashsharah (the ten Sahaabah who were given the certain promise of Paradise) with the exception of Ali (may Allaah be pleased with him). Hence they will say Nine plus one instead of ten.
Certain sounds, such as the voice of a crow or the sound of an ambulance or fire truck.
Frightening or disturbing dreams.
Colours, such as the colour of blood, or yellow.
When the eyelashes of the left eye tremble involuntarily, they say, Something bad is going to happen to us.
Calling a child by the name of a living person, such as the father or mother and so on.
Witnessing an accident or a fire in the morning.
Seeing ones wifes mother in the morning.
When the right hand or right foot itches.
 The virtue of tawakkul (putting ones trust in Allaah) and not indulging in tiyarah. The Prophet ( peace and blessings of Allaah be upon him) said: Seventy thousand people will enter Paradise without being called to account and without being punished. Among the virtues of these people, he described them as not believing in tiyarah and as putting their trust in Allaah. (Reported by Muslim).
 Condemnation of tiyarah and explanation that it is a kind of shirk. Ibn Masood (may Allaah be pleased with him) said: The Messenger of Allaah (peace and blessings of Allaah be upon him) said: Al-tiyarah is shirk, and he said it three times. (Reported by Abu Dawood and others, and classed as saheeh by al-Albaani).
Imraan ibn Husayn (may Allaah be pleased with him) said: The Messenger of Allaah (peace and blessings of Allaah be upon him) said: He is not one of us who does tiyarah or has it done for himself Al-Albaani said: Its isnaad is hasan. Ibn al-Qayyim said: Tiyarah is a kind of shirk and a way in which the Shaytaan influences and scares a person. It is very serious for the one who takes it to heart and pays too much attention to it, but it is insignificant for the one who pays no attention to it and is not concerned about it.
 Negation of tiyarah and superstition. Abu Hurayrah (may Allaah be pleased with him) said: The Messenger of Allaah (peace and blessings of Allaah be upon him) said: There is no adwaa (contagion) or tiyarah, but I like righteous fal.(Muslim). And he said, No adwaa, no tiyarah, no haamah, and no Safar. (Reported by al-Bukhaari and Muslim).
Muaawiyah ibn al-Hakam al-Salami reported that he said to the Messenger of Allaah (peace and blessings of Allaah be upon him): Some of us believe in tiyarah. He said, That is something that any of you may feel in himself, but it should not stop you from doing anything.(Muslim).
So the Prophet (peace and blessings of Allaah be upon him) explained that any anxiety suffered because of tiyarah is all in the mind and has nothing to do with the object that caused the fear. It is the persons own illusion, fear and shirk that is affecting him and stopping him from doing what he wants to do, not the thing that he saw or heard. Whoever adheres firmly to the bonds of Tawheed and puts all his trust in Allaah, thus nipping the ideas of tiyarah in the bud before they take hold, will be successful and happy in this world and the next.
In a saheeh hadeeth, the Prophet (peace and blessings of Allaah be upon him) said: Leave any ideas of tiyarah as they are [i.e., do not take them any further].(Saheeh Abi Dawood). What this hadeeth means is that the Prophet (peace and blessings of Allaah be upon him) wanted them not to pay attention to such ideas, but to leave them alone, as Allaah had made them, because they can bring neither benefit nor harm.
Ibn Jareer said: What this means is to leave birds (tayr) alone without shooing them away, and carry on with one's own business, because shooing them away does not bring any benefit or ward off any harm.
Ikrimah (may Allaah have mercy on him) said: We were sitting with Ibn Abbaas when a bird flew over us and screeched. A man who was there said, Good! Ibn Abbaas said to him, It is neither good nor bad. He hastened to rebuke him lest he think that it had any influence for good or evil.
Taawoos set out on a journey with one of his friends, and a crow screeched. The man said, Good! Taawoos said, What is the good in that? Do not accompany me any further.
Ibn Abd al-Hakam said: Muzaahim said, When Umar ibn Abd al-Azeez set out from Madeenah, I looked and saw that the moon was in Hyades [a group of stars in Taurus], and I did not want to tell him that, so I just said to him, Look how beautiful the moon looks tonight. Umar looked, and saw that the moon was in Hyades, and said, It is as if you wanted to tell me that the moon was in Hyades. O Muzaahim, we do not go out by the help of the sun or the moon; we go out by the help of Allaah, al-Waahid, al-Qahhaar.
 The limits of tiyarah. The kind of tiyarah that makes a person go ahead with his plans or stops him from going ahead is the kind of tiyarah that is prohibited. As for the good omens (fal) that the Prophet (peace and blessings of Allaah be upon him) liked, this is a kind of optimism that a person does not feel dependent upon, unlike things that may make a person either go ahead or change his plans, in which a person is in a sense depending upon it. And Allah knows best.
 Kafaarah (expiation) for one who engages in tiyarah. Imaam Ahmad reported in his Musnad and Ibn al-Sunni also reported with a saheeh isnaad from Abd-Allaah ibn Amr that the Messenger of Allaah (peace and blessings of Allaah be upon him) said: Whoever lets tiyarah stop him from doing something is guilty of shirk. They said, What is the kafaarah for that? He said, To say: Allaahumma la khayra illaa khayruka wa laa tayra illaa tayruka wa laa ilaaha ghayruka (O Allaah, there is no good except Your good, no birds except Yours, and there is no god beside You).
no birds except Yours means: the birds are part of Your creation, they can bring neither benefit nor harm, and the only One Who can bring benefit or harm is You, may You be glorified.
 Remedies for tatayyur:
(a) tawakkul, which means delegating all ones affairs to Allaah and relying on Him, whilst at the same time taking the necessary means and precautions. This is an obligation which must be done purely and sincerely for Allaah, because it is one of the best forms of worship and highest levels of Tawheed. Allaah says (interpretation of the meanings): and put your trust in Allaah, if you are believers indeed. [al-Maaidah 5:23] and And put yout trust in the Ever-Living One Who dies not, and glorify His Praises, and Sufficient is He as the All-Knower of the sins of His slaves. [al-Furqaan 25:58]. Putting ones trust in Allaah is one of the greatest and most important ways of getting rid of pessimism and superstition and other matters pertaining to shirk.
(b) Knowing that everything that happens, happens by the decree of Allaah. Blessings and calamities alike are covered by the will and decree of Allaah, as He says (interpretation of the meaning): No calamity befalls on the earth or in yourselves but is inscribed in the Book of Decrees (al-lawh al-mahfooz), before We bring it into existence. Verily, that is easy for Allaah. [al-Hadeed 57:22]. Thus a person may be reassured about these matters, and there is no need for tatayyur or tiyarah, because good and bad alike are subject to the will and decree of Allaah.
(c) Istikhaarah. This is one of the greatest forms of worship and is complete tawakkul or dependence on Allaah. It is the alternative to tatayyur and tiyarah. The Prophet (peace and blessings of Allaah be upon him) used to teach his Companions to make istikhaarah for all their affairs just as he used to teach them the soorahs of the Quraan.
(d) Moving away from places which one thinks are unlucky. Here we are talking about doubt, not certainty. Anas ibn Maalik (may Allaah be pleased with him) said: A man said, O Messenger of Allaah, we lived in a house where our number was great and our wealth was abundant, then we moved to a house where our numbers dwindled and our wealth decreased. The Messenger of Allaah (peace and blessings of Allaah be upon him) said: Leave it, for it is bad. (Reported by Maalik, Abu Dawood, al-Bukhaari in al-Adab al-Mufrad, and classed as hasan by al-Albaani).
Leave it, for it is bad Ibn Abd al-Barr said: I think that he said it lest they adhere to thoughts of tiyarah. Al-Baghawi said: He told them to move away from it because they did not like it and did not feel comfortable; if they moved, the things they were feeling would go away. He did not tell them to move because the house was the cause of the problems.
But the Creator made that the time for His decree to be carried out. suggested by Ibn al-Arabi al-Maaliki.
(e) Fal (good omen). This is the opposite of tiyarah, for example when a man who is sick hears another addressing him as Ya saalim (O healthy one)!. The Messenger of Allaah (peace and blessings of Allaah be upon him) said: There is no adwaa (contagion) and no tiyarah, but I like righteous fal, a good word. (Reported by al-Bukhaari and Muslim).
The difference between fal and tiyarah is that fal involves thinking in positive terms about Allaah, whereas tiyarah involves the opposite, so for this reason it is disliked.
There is another issue here: if a person puts his trust in Allaah and goes ahead with his plans, then disaster strikes and harm befalls him, how can this happen when he thought of Allaah in positive terms? Our answer is that this is a test, not an omen or tiyarah; the believer is tested in accordance with the level of his faith.
Haafiz al-Hakami said: One of the conditions of fal is that it is not something that a person relies on or tries to figure out; it is just a coincidence that happens to a person without him thinking about it. It is a particularly loathsome form of bidah to try to find fal in the Quraan [by opening it at random]. The one who takes the Verses of Allaah as a joke or idle entertainment is surely doing wrong. If a person tries to figure out fal and use it to get good luck, this is tiyarah, like using arrows to seek luck or a decision.
O Allaah, we seek refuge with You from associating anything knowingly with You, and we seek Your forgiveness for that which we do unknowingly.
Al-Qawl al-Mufeed ala Kitaab al-Tawheed. Ibn Uthaymeen.
Al-Tiyarah wal-Fal. Mahmoud al-Jaasim
Tayseer al-Azeez al-Hameed Sharh Kitaab al-Tawheed. Sulaymaan ibn Abd-Allaah.
Fath al-Baari. Ibn Hajar.
Fath al-Majeed Sharh Kitaab al-Tawheed. Abd al-Rahmaan ibn Hasan.
Maaarij al-Qubool. Al-Hakam.
Miftaah Daar al-Saaadah. Ibn al-Qayyim.