whether in affirmation or denial, he reinforces it by swearing by whatever he regards as most exalted. From the earliest ages people have believed that the being invoked in the oath exercises power over the swearer, able to benefit or harm him through natural means and by causes beyond nature. If the swearer fulfils what he has vowed, that being is thought to be pleased with him and to grant him benefit; but if he fails, it is displeased and harms him. For this reason, swearing by anything other than Allah or His attributes constitutes shirk (associating partners with Allah).
2 – The hadith establishes that whoever intends to take an oath must swear by Allah alone. Ibn Masʿūd (may Allah be pleased with him) said, “For me to swear by Allah while lying is dearer than to swear truthfully by anyone other than Him.” Shaykh al-Islām explained, “The virtue of tawḥīd (pure monotheism) is greater than the virtue of truthfulness, and the sin of lying is lighter than the sin of shirk.” Allah the Exalted says, “Indeed, Allah does not forgive that partners be associated with Him, but He forgives what is less than that” ⦗al-Nisāʾ 4:48⦘. Al-Māwardī said, “It is impermissible for anyone to swear by other than Allah—whether by a divorce pronouncement, the emancipation of a slave, or a vow.” The hadiths clearly indicate the prohibition. Among them is the report recorded by Abū Dāwūd (3251) and al-Ḥākim (1/65) from Ibn ʿUmar: the Prophet ﷺ said, “Whoever swears by anything other than Allah has disbelieved.”
3 – It is likewise forbidden to swear by renouncing Islam—such as saying, “I am free of Islam,” “I am free of the religion,” “I am a Jew,” “I am a Christian,” and the like. Abū Dāwūd (3258) and al-Nasāʾī (3772) recorded, with a chain that meets Muslim’s criterion, from Buraydah that the Prophet ﷺ said: “Whoever swears, saying, ‘I am free of Islam,’ if he is lying he will be as he claimed; but if he is truthful, he will never return to Islam unscathed.”
4 – If swearing by one’s forefathers is prohibited and unlawful, then swearing by the andād—the idols—is even more severely forbidden and carries an even graver penalty.