a major sin. This is why Ibn Mas‘ud, may Allah be pleased with him, said: “That I should swear by Allah falsely is dearer to me than that I should swear truthfully by other than Him.” (1) Shaykh al-Islam, may Allah have mercy on him, said: “For the evil of shirk, even when minor, is greater than the evil of a sin, even when major.”
His statement: “No expiation is due for it,” because it is an unlawful oath, and that which is not legislated carries none of its legal effects. The Messenger of Allah ﷺ said: “Whoever performs a deed that is not in accordance with our matter will have it rejected.” (2) Everything that contravenes the Sacred Law has no legal effect.
If you say: Swearing by other than Allah is forbidden and constitutes shirk, yet the most God-fearing of people—Muhammad, the Messenger of Allah ﷺ—did it. A Bedouin came to him and asked him about the rites of Islam, and he informed him. The man then said, “By Allah, I shall neither add to this nor diminish from it.” The Prophet ﷺ said: “He will prosper, by his father, if he speaks the truth.” (3) So how can we say that swearing by other than Allah is forbidden or shirk, when shirk is impossible for the Prophets, since it utterly contradicts their call? They call people to tawhid, whereas shirk opposes it—even minor shirk. If it is major shirk, it negates tawhid at its very foundation; and if it is minor shirk, it negates its perfection. So how could the Messenger ﷺ swear by other than Allah in saying, “He will prosper, by his father”?
The scholars have given several answers to this: