Mishkat al-Masabih #3309

‘Imran b. Husain told that he heard God’s Messenger say, “Vows are of two kinds, so if anyone vows to do an act of obedience, that is for God and must be fulfilled; but if anyone vows, to do an act of disobedience, that is for the devil and must not be fulfilled, but he must make atonement for it to the extent he would do in the case of an oath.”