Riyad as-Salihin 1714
The Book of the Prohibited actions
Illegality of Swearing Falsely
'Abdullah bin 'Amr bin Al-As (May Allah be pleased with them) said: The Prophet (ﷺ) said, "Of the major sins are: Associating anything in worship with Allah, disobedience to the parents, killing without justification and taking a false oath (intentionally)." [Al- Bukhari]. Another narration is: A bedouin came to the Prophet (ﷺ) and asked him: "O Messenger of Allah, what are the cardinal sins?" He (ﷺ) replied, "Associating anything with Allah in worship." The man asked: "(What is) next?" The Messenger of Allah (ﷺ) replied, "Al-Yamin Al-Ghamus." He asked: "What do you mean by Al-Yamin Al-Ghamus?" The Messenger of Allah (ﷺ) replied, "Swearing falsely to usurp the property of a Muslim."