The prohibition against swearing by a creature like the Prophet, the Ka'ba, the angels, heaven, fathers, life, the spirit, the head, the life of the Sultan, the blessing of the Sultan, one's land, and trustworthiness. It is the strongest possible prohibition

Riyad as-Salihin (The Meadows of the Righteous)

by Imam Nawawi

314. Chapter: The prohibition against swearing by a creature like the Prophet, the Ka'ba, the angels, heaven, fathers, life, the spirit, the head, the life of the Sultan, the blessing of the Sultan, one's land, and trustworthiness. It is the strongest possible prohibition

1707. Ibn 'Umar reported that the Prophet, may Allah bless him and grant him peace, said, "Allah Almighty forbids you to swear an oath by your fathers. If someone swears an oath, he should swear by Allah or be silent." [Agreed upon]

1708. 'Abdu'r-Rahman ibn Samura reported that the Messenger of Allah, may Allah bless him and grant him peace, said, "Do not swear by idols or by your fathers." [Muslim]

1709. Burayda reported that the Messenger of Allah, may Allah bless him and grant him peace, said, "Anyone who swears by trustworthiness is not one of us." [Abu Dawud]

1710. Burayda reported that the Messenger of Allah, may Allah bless him and grant him peace, said, "If anyone swears an oath saying, 'I am no longer a Muslim [if I am not speaking the truth],' if he is lying, it is as he said and if he is speaking the truth, he will not return to Islam unblemished." [Abu Dawud]

1711. Ibn 'Umar reported that he heard a man say, "No, by the Ka'ba." Ibn 'Umar said, "Do not swear by other than Allah. I heard the Messenger of Allah, may Allah bless him and grant him peace, say, 'Anyone who swears by other than Allah has rejected - or associated.'" [at-Tirmidhi]