1707/1 - Ibn ‘Umar (may Allah be pleased with him and his father) reported that the Prophet (may Allah’s peace and blessings be upon him) said: “Indeed, Allah Almighty forbids you from swearing by your fathers. So, he who wants to swear should swear by Allah or keep silent.” [Narrated by Al-Bukhāri and Muslim]
In another authentic narration: “So, he who wants to swear should swear by none but Allah or remain silent.”
1708/2 - ‘Abdur-Rahmān ibn Samurah (may Allah be pleased with him) reported that the Messenger of Allah (may Allah’s peace and blessings be upon him) said: “Do not swear by the Tawāghi (idols) or your fathers.” [Narrated by Muslim]
Tawāghi: the plural of Tāghiyah, which means idol. This term is used in a Hadīth reading: “This is the Tāghiyah of Daws”, i.e. their idol. Another narration, not by Muslim, includes the term Tawāghīt, the plural of Tāghūt, which means the devil and idol.
1709/3 - Buraydah (may Allah be pleased with him) reported that the Prophet (may Allah’s peace and blessings be upon him) said: “He who swears by the trust is not one of us.” [Narrated by Abu Dāwūd with an authentic Isnad; Sahīh (authentic)]
1710/4 - He also reported that the Messenger of Allah (may Allah’s peace and blessings be upon him) said: “Anyone who swears saying: ‘I am innocent of Islam,’ if he is lying, he will be as he said; and if he is telling the truth, his Islam will be defective.” [Narrated by Abu Dāwūd]
1711/5 - Ibn ‘Umar (may Allah be pleased with him and his father) reported that he heard a man saying: “No, by the Ka‘bah.” He said to him: “Do not swear by other than Allah, for I heard the Messenger of Allah (may Allah’s peace and blessings be upon him) say: ‘Whoever swears by other than Allah has become a disbeliever, or a polytheist.’” [Narrated by Al-Tirmidhi; he classified it as Hasan (sound)]
Some scholars took his words “has become a disbeliever or a polytheist” to refer to the gravity of the sin - like the Prophet’s statement: “Ostentation is polytheism.”
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1) It is prohibited to swear by other than Allah Almighty, which is an act of polytheism.
2) A person should be keen not to swear by any creature, even a great one, or to ask someone to take such an oath that throws him into polytheism.
3) The prohibition of swearing by other than Allah Almighty demonstrates the exclusive right of the Almighty Lord to be worshiped alone. No creature, no matter how great he may be, should be made equal to Allah by way of swearing.
As part of swearing by Allah Almighty, it is permissible to swear by the Qur’an or the Mus-haf (bound copy of the Qur’an), for it is the speech of Allah and one of His attributes. In fact, the swearer does not mean the papers and the ink, which are both created.
As for swearing by the trust, as some people say: “the trust, the trust”, it is a form of swearing on which we have cited the Hadīth: “He who swears by the trust is not one of us.” Therefore, a person should try to correct his speech and regulate it in accordance with the Shariah and enjoin others to do the same - in fulfillment of monotheism, which is Allah’s right upon His servants.