I heard number 7 is lucky; number 14 or 13 is unlucky. Are they true?.
What you mention is not true; there is no connection between numbers and luck. Regarding the numbers 13 and 14, or any other numbers or days, months or colours, as unlucky comes under the heading of tatayyur (superstitious belief in bird or other omens) which is forbidden in Islam.
Al-Bukhaari (5776) and Muslim (2224) narrated from Anas ibn Maalik (may Allaah be pleased with him) that the Prophet (peace and blessings of Allaah be upon him) said: “There is no ‘adwa (transmission of infectious disease without the permission of Allaah) and no tiyarah (superstitious belief in bird omens), but I like optimism.” They said, “What is optimism?” He said, “A good word.”
Ahmad (4194), Abu Dawood (3910), al-Tirmidhi (1614) and Ibn Maajah (3538) narrated that ‘Abd-Allaah ibn Mas’ood said: The Messenger of Allaah (peace and blessings of Allaah be upon him) said: “Tiyarah (belief in evil omens) is shirk.” Classed as saheeh by al-Albaani in Saheeh Abi Dawood.
Ahmad (7045) and al-Tabaraani narrated that ‘Abd-Allaah ibn ‘Amr said: 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).”
Classed as hasan by al-Arna’oot and as saheeh by al-Albaani in Saheeh al-Jaami’, no. 6264.
Al-Tabaraani narrated in al-Kabeer from ‘Imraan ibn Husayn that the Messenger of Allaah (peace and blessings of Allaah be upon him) said: “He is not one of us who practices augury [seeking omens in birds] or has that done for him, or who practices divination or has that done for him, or who practices witchcraft or has that done for him.” Classed as saheeh by al-Albaani in Saheeh al-Jaami’, no. 5435.
Al-Nawawi (may Allaah have mercy on him) said in Sharh Muslim, no. 2224:
Tatayyur (belief in bad omens) is pessimism, and is based on something disliked, be it a word or action or something seen… They used to startle gazelles and birds to make them move; if they went to the right they would regard that as a good omen and go ahead with their journeys or other plans, but if they went to the left they would cancel their journeys and plans, and regard that as a bad omen. So it would often prevent them from doing things that were in their interests. Islam cancelled out all that and forbade it, and said that it had no effect, whether good or bad. This is what is meant by the words of the Prophet (peace and blessings of Allaah be upon him): “There is no tiyarah (superstitious belief in bird omens),” and in another hadeeth, “Tiyarah is shirk” – i.e., the belief that it can bring benefit or harm, if they act upon it believing that it has any effect then this is shirk, because they think that it has an effect on what one does or that it can make things happen.
With regard to fa’l or belief in good omens, the Prophet (peace and blessings of Allaah be upon him) described it as a good and righteous word.
The scholars said: fa’l may be with regard to good or bad things, but it usually has to do with good things, but tiyarah can only have to do with bad things. They said: It may be used as a metaphor for good things… And the scholars said: He liked fa’l because if a person hopes for the benefit and bounty of Allaah, whether for a strong or weak reason, he will be in a good state, and if he is mistaken in his hope, then hope is still good for him. But if he loses hope in Allaah then that is bad for him. Tiyarah means thinking badly and expecting calamity. One example of fa’l is when a person is sick and he hears optimistic words such as “Yaa saalim (O healthy one)!”, or when a person is looking for something and he hears someone say “Yaa waajid (O finder).” So this fills his heart with the hope that he will recover or find what he is looking for. And Allaah knows best.
End quote from al-Nawawi, may Allaah have mercy on him.
Shaykh al-‘Uthaymeen (may Allaah have mercy on him) said: If the Muslim pays any heed to these things, one of two scenarios must apply, the first of which is that he responds to it, so he either goes ahead or cancels his plan, in which case he is basing his actions on something that is invalid; and the second of which is that he does not respond, so he goes ahead and does not care about it, but in his heart there is still some worry or anxiety. Even though this is less serious than the first scenario, he should not pay any attention to these things at all, and he should depend on Allaah.
Majmoo’ al-Fataawa, 2/113
The point is that it is not permissible to regard any numbers as unlucky. Whoever reads or hears a number and regards that as a bad omen has committed tatayyur which is forbidden. The expiation (kafaarah) for that, as stated in the hadeeth quoted above, is 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.