1707. Ibn `Umar (May Allah be pleased with them) said: The Prophet (sallallaahu ’alayhi wa sallam) said, "Allah has prohibited you from taking an oath by your fathers. He who must take an oath, may do so by swearing in the Name of Allah or he should remain silent.''
[Al-Bukhari and Muslim].
Commentary: We learn from this Hadith that taking the oath of one's ancestors is prohibited. In the forthcoming Ahadith one is also forbidden from taking the oath of false gods and devils.
1708. `Abdur-Rahman bin Samurah (May Allah be pleased with him) said: The Messenger of Allah (sallallaahu ’alayhi wa sallam) said, "Swear neither by the name of Taghut (i.e., false deities, false leaders, etc.) nor by your fathers.''
1709. Buraidah (May Allah be pleased with him) said: The Messenger of Allah (sallallaahu ’alayhi wa sallam) said, "He who swears by Amanah (trust) is not one of us.''
[Abu Dawud with authentic Isnad].
Commentary: The oath of Amanah means to say "By Amanah'' as one says "By Allah''. This is prohibited for the reason that one can take the oath of Allah or any of His Attributes. Amanah is one of the Commandments of Allah and an obligation prescribed by Him, like Salat, Saum, Hajj etc. In this way, the Commandments of Allah assume the resemblance of His Glorious Names and Attributes, which is not correct.
1710. Buraidah (May Allah be pleased with him) reported: The Messenger of Allah (sallallaahu ’alayhi wa sallam) said, "If anyone swears that in such and such case he will be free from Islam and afterwards he turns out to be a liar, he will be as he has sworn; but if he is speaking the truth, he will not revert safely to Islam.''
Commentary: What this Hadith tells us is that if someone says "If I do such and such thing, I will be a Kafir'', now, if he really meant that if he did that he will adopt Kufr, then he will at once become a Kafir. But if he meant that he will strictly adhere to Islam and never take the way of Kufr, he will not become a Kafir but the style in which he said it was certainly wrong. Therefore, he must make repentance and beg forgiveness from Allah for it. It will be better if he recites again Kalimahtush-Shahadah to renew his Faith.
1711. Ibn `Umar (May Allah be pleased with them) said: I heard a man saying: "No, by the Ka`bah.'' I admonished him: "Do not swear by any thing besides Allah, for I heard the Messenger of Allah (sallallaahu ’alayhi wa sallam) saying, `He who swears by anyone or anything other than Allah, has indeed committed an act of Kufr or Shirk'.''
[Some `Ulama' are of the opinion that the words of the Prophet (sallallaahu ’alayhi wa sallam) that "He who swears by anyone or anything other than Allah has indeed committed an act of Kufr or Shirk,'' are in the nature of extreme admonition. And in fact, it is not Shirk. The same applies to the saying of the Prophet (sallallaahu ’alayhi wa sallam), who said, "showing off is Shirk.'']
Commentary: Imam An-Nawawi has regarded the saying "showing off is Shirk'' as Hadith is not narrated in these words. It is, however, true that what the Prophet (sallallaahu ’alayhi wa sallam) has stated about the evil and sinfulness of showing off implies that it is also a (minor) Shirk. For instance he stated that "He who kept fast or offered Salat for mere show, has indeed committed Shirk.'' In any case, to take oath of anyone other than Allah is strictly forbidden. It is, therefore, necessary to abstain from swearing by other than Allah. Unfortunately, such oaths are very common and people do not realize that they are prohibited and unlawful.