It is soundly narrated from the Prophet (blessings and peace of Allah be upon him) that he forbade swearing by anyone or anything other than Allah, may He be Exalted.
It was narrated from Ibn `Umar (may Allah be pleased with him) that the Prophet (blessings and peace of Allah be upon him) said: “Whoever wants to swear, let him not swear by anything but Allah.” Quraysh used to swear by their fathers, but he said: “Do not swear by your fathers.” Narrated by al-Bukhari, 3836; Muslim, 1646.
According to another report narrated by al-Bukhari, 2679, and Muslim, 1646, the Prophet (blessings and peace of Allah be upon him) said: “Whoever wants to swear, let him swear by Allah or else remain silent.”
Ibn `Abd al-Barr (may Allah have mercy on him) said:
The scholars are unanimously agreed that swearing by anyone or anything other than Allah is disliked (makruh) and not allowed; it is not permissible for anyone to swear by that.
End quote from At-Tamhid, 14/367.
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said:
As for swearing by created things, such as swearing by the Ka`bah, or by the grave of the shaykh, or by the favour of the ruler, or by the sword, or by the status of some created being before Allah, I do not know of any difference of opinion among the scholars regarding the fact that swearing by such things is disliked and not allowed, and that going against what one swore about when saying those words is not regarded as breaking an oath and does not require expiation for breaking an oath. But is swearing by such things prohibited or is it disliked in the sense that one should not do it?
Regarding that there are two views in the madhhab of Ahmad and others; the more sound view is that it is prohibited.
End quote from Majmu` al-Fatawa, 35/243.
Ibn al-Qayyim (may Allah have mercy on him) said:
One of the major sins is swearing by something or someone other than Allah, as the Messenger of Allah (blessings and peace of Allah be upon him) said: “Whoever swears by something other than Allah has committed an act of shirk [associating something or someone with Allah].” He is mistaken who says that doing that is disliked (makruh), when the Lawgiver describes it as shirk; thus the degree of sin of such an oath is greater than that of major sin.
End quote from I`lam al-Muwaqqi`in, 6/571-572.
The hadith mentioned was narrated by Ibn `Umar, who said: I heard the Messenger of Allah (blessings and peace of Allah be upon him) say: “Whoever swears by something other than Allah has committed an act of shirk [associating something or someone with Allah].” Narrated by Abu Dawud, 3251; and by at-Tirmidhi, 1535, who said: This is a sound (hasan) hadith. It was classed as authentic (sahih) by al-Albani in Irwa’ al-Ghalil, 8/189.
This shirk may be major, or it may be minor and prohibited, but it does not put the one who does it beyond the bounds of Islam.
It is major shirk if the individual regards what he swears by as being equal to Allah in deserving veneration and having the power to benefit or harm, as some grave worshippers do when they swear by the occupant of the grave and believe that he has the power to avert harm or to bring benefit in an unknown manner, so they call on him to be a witness that they are telling the truth.
Al-Hafiz Ibn Hajar (may Allah have mercy on him) said:
If he believes that what he is swearing by is deserving of veneration, as he believes about Allah, then it is prohibited to swear by it, and by believing that,he becomes a disbeliever, and the hadith mentioned is applicable to people like him.
End quote from Fat-h al-Bari, 11/531.
Shaykh `Abd ar-Rahman al-Mu`allimi (may Allah have mercy on him) said:
This type of swearing an oath indicates how much the one who is swearing the oath venerates the one by whom he swears it, and believes that he has unseen powers, so that the one who swears by him will gain benefit in an unseen manner if he fulfils his oath and speaks the truth, but if he does not fulfil it he will be punished by the one by whom he swore his oath, and the one by whom he swore the oath will benefit him in an unseen manner by enabling him to get his right if he has a right…
and similarly, swearing by an idol indicates that the one who swears the oath venerates it and believes that it has unseen power…
Once this is established, it becomes clear that swearing in this manner involves submission to and veneration of that by which the individual swears, seeking thereby benefit for the one who swears in this manner, or for the one by whom the oath is sworn. This submission and veneration is worship, as established above, and any act of worship for which there is no evidence in the religious texts is worship for someone other than Allah, and worship for someone other than Allah is disbelief and shirk.
End quote from Athar ash-Shaykh `Abd ar-Rahman al-Mu`allimi, 3/1018.
Swearing by someone or something other than Allah is minor shirk if it does not reach this level of veneration.
Shaykh Ibn `Uthaymin (may Allah have mercy on him) said:
Swearing by someone or something other than Allah is major shirk if the one who swears in this manner believes that that by which he swears is equal to Allah, may He be Exalted, in terms of veneration and respect. Otherwise it is minor shirk.
End quote from Al-Qawl al-Mufid, 2/214.
It says in Fatawa al-Lajnat ad-Da’imah – Vol 1 (23/56):
Swearing by honesty is swearing by something other than Allah, and swearing by something other than Allah is minor shirk and one of the greatest of majors sin, because of the report narrated by `Abdullah ibn `Umar ibn al-Khattab (may Allah be pleased with them both), who said: The Messenger of Allah (blessings and peace of Allah be upon him) said:
“Whoever swears by something other than Allah has committed an act of disbelief or an act of shirk [associating something or someone with Allah].” Ibn Mas`ud (may Allah be pleased with him) said: If I were to swear by Allah and say something false, that would be dearer to me than swearing by anything other than Him and saying something true.
Al-Lajnat ad-Da’imah lil-Buhuth al-`Ilmiyyah wal-Ifta’.
`Abdullah ibn Sulayman ibn Munayyi`, `Abdullah ibn `Abd ar-Rahman ibn Ghadyan, `Abd ar-Razzaq `Afifi. End quote.
Secondly:
It was narrated that Talhah ibn `Ubaydillah said: A man from among the people of Najd, with dishevelled hair, came to the Messenger of Allah (blessings and peace of Allah be upon him), and we could hear the sound of his voice but we could not understand what he was saying, until he drew close to the Messenger of Allah (blessings and peace of Allah be upon him), and we realized that he was asking about Islam. The Messenger of Allah (blessings and peace of Allah be upon him) said: “Five prayers each day and night.” He said: Do I have to do any (prayers) other than that? He said, “No, unless you do them voluntarily. And fasting the month of Ramadan.” He said: Do I have to do any (fasting) other than that? He said: “No, unless you do it voluntarily.” And the Messenger of Allah (blessings and peace of Allah be upon him) mentioned zakah, and he said: “Do I have to do anything other than that?” He said, “No, unless you do it voluntarily.” The man left, saying: By Allah, I shall not do any more than this or any less. The Messenger of Allah (blessings and peace of Allah be upon him) said: “He will succeed, by his father, if he is speaking the truth” or, “He will enter Paradise, by his father, if he is speaking the truth.” Narrated by Muslim, 11.
It was narrated that Abu Hurayrah said: A man came to the Prophet (blessings and peace of Allah be upon him) and said: O Messenger of Allah, what kind of charity brings the greatest reward? He said: “By your father, I shall tell you. Give charity when you are healthy and inclined to be stingy, fearing poverty and hoping to live (long), and do not put it off until (your soul) reaches the throat and you say: ‘Such and such is for So and so, and such and such is for So and so.’ No, it has already become the property of So and so.” Narrated by Muslim, 1032.
It was narrated that Abu Hurayrah said: A man said: O Messenger of Allah, which of the people is most deserving of my good companionship? He said: “Your mother, then your mother, then your mother, then your father, then the next closest and the next closest.” Narrated by Muslim, 2548. Then he narrated another report after it, in which the words “Yes, by your father, I shall tell you” are added.
These hadiths include words swearing by fathers.
The scholars gave several answers regarding this matter:
Some of the scholars were of the view that these phrases “by his father” and “by your father” – are weak (da`if) and are not soundly narrated, and that those who included them in these hadiths were mistaken.
For example, Ibn `Abd al-Barr (may Allah have mercy on him) said:
If anyone quotes as evidence a hadith narrated from Isma`il ibn Ja`far, from Abu Suhayl Nafi` ibn Malik ibn Abi `Amir, from his father, from Talhah ibn `Ubaydillah, about the story of the Najdi Bedouin, which says that the Prophet (blessings and peace of Allah be upon him) said: “He will succeed, by his father, if he is speaking the truth,”
It should be said to him: This wording is not known in this hadith, because it was narrated by one whose hadith is not reliable (and cannot be quoted as evidence). This hadith was narrated by Malik and others from Abu Suhayl, and they did not include that phrase in it. And this hadith was narrated from Isma`il ibn Ja`far with this phrase – “He will succeed, by Allah, if he is speaking the truth” or “He will enter paradise, by Allah, if he is speaking the truth” – and this is more correct than the report which includes the phrase “by his father,” because that is an objectionable and odd phrase that is to be rejected on the basis of the sound reports. And Allah is the source of strength.
End quote from At-Tamhid, 14/367.
Shaykh al-Albani (may Allah have mercy on him) explained that these phrases were not soundly narrated, in his book As-Silsilat ad-Da`ifah, 10/750-768.
Even assuming that these reports are sound, the context of the hadith confirms that it was not meant to be an oath of the type that is indicative of veneration of the one by whom the oath is sworn.
That is because (in this reports) the Prophet (blessings and peace of Allah be upon him) was not swearing by his own father, `Abdullah, so he did not say ‘by my father’, such that one might think that he was swearing by his own father and that he mentioned his father in his oath by way of venerating him because he was his father. Rather he mentioned the father of the one to whom he was speaking, who was most likely a polytheist, so there is no reason to suspect that he could be venerating him at all. Rather it was a way of emphasizing and affirming what he was saying, as was customary among the Arabs, without intending it as an oath. This is like other phrases that they customarily said, such as “Woe to you!” and “May your mother be bereft of you!” – They did not mean such phrases literally.
Al-Khattabi (may Allah have mercy on him) said:
The phrase “He will succeed, by his father” is something that the Arabs customarily said and they used it a great deal in their conversations, with the intention of affirming what they were saying…
The Arabs may use this phrase in their speech for two reasons, the first of which is by way of veneration and the other is by way of emphasizing what they are saying, without intending to swear an oath.
End quote from Ma`alim as-Sunan, 1/121.
An-Nawawi (may Allah have mercy on him) said:
The Prophet’s words “He will succeed, by his father” are not an oath; rather this is a phrase that the Arabs habitually said when speaking, without intending it as an actual oath. The prohibition only applies when it is intended as an actual oath, because that implies veneration of the one by whom the oath is sworn, which is a kind of veneration that should be for Allah, may He be Glorified and Exalted, alone. This is the right answer.
End quote from Sharh Sahih Muslim, 1/168.
To sum up:
There are different views as to whether this objectionable phrase in the hadiths referred to above is soundly narrated. However, it is not clearly intended to be an oath, so it is not correct to use such reports to contradict the clear, soundlt-narrated hadiths which forbid swearing by anything other than Allah, may He be Exalted.
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said:
It is proven in clear texts that are soundly narrated from the Prophet (blessings and peace of Allah be upon him) that it is not permissible to swear by any created being or thing, and there is no differentiation in that regard between the angels, the prophets, the righteous and anyone else.
End quote from Majmu` al-Fatawa, 1/291.
Thirdly:
If a Muslim swears by something or someone other than Allah without realizing and does not do that intentionally – such as when someone who was not a practising Muslim for many years, then he repented to Allah, may He be Exalted, says by a slip of the tongue words that he was used to saying before he repented, without him meaning to say them – then in that case he will not be called to account for that.
This is indicated by the general meaning of the verses in which Allah, may He be Exalted, says:
{Allah does not call you to account for what is unintentional in your oaths, but He will call you to account for what your hearts have earned. And Allah is Forgiving and Forbearing} [Al-Baqarah 2:225]
{Allah does not place on any soul a burden greater than it can bear. It will have [the consequence of] what [good] it has gained, and it will bear [the consequence of] what [evil] it has earned. “Our Lord, do not hold us accountable if we have forgotten or erred. Our Lord, and lay not upon us a burden like that which You laid upon those before us. Our Lord, and burden us not with that which we have no ability to bear. And pardon us; and forgive us; and have mercy upon us. You are our protector, so give us victory over the disbelieving people.”} [Al-Baqarah 2:286].
Shaykh Muhammad al-Amin ash-Shinqiti (may Allah have mercy on him) said:
Regarding the words {Our Lord, do not hold us accountable if we have forgotten or erred}, Allah did not state whether He answered their supplication or not. But He indicated that He has answered it by saying regarding error: {And there is no sin on you for that in which you have erred but [only for] what your hearts intended. And ever is Allah Forgiving and Merciful} [Al-Ahzab 33:5]. And He indicated that He has answered it with regard to forgetfulness by saying: {If the Shaytan causes you to forget, then as soon as you remember, do not sit with people who are given to wrongdoing} [al-An`am 6:68]. This clearly means that before remembering, there is no sin on him for that…
And it is soundly narrated in Sahih Muslim that the Prophet (blessings and peace of Allah be upon him) recited the verse { Our Lord, do not do not hold us accountable if we have forgotten or erred } [and said:] “Allah, may He be Exalted, said: Yes [I grant that].”
End quote from Adwa’ al-Bayan, 1/312.
And Allah knows best.