Muwatta Malik 1018

Yahya related to me from Malik from Hisham ibn Urwa from his father that A'isha, umm al-muminin said, "Rashness in oaths is that a man says, 'By Allah, No! by Allah!' " i.e. out of habit. Malik said, "The best of what I have heard on the matter is that rashness in oaths is that a man take an oath on something to show that he is certain that it is like he said, only to find that it is other than what he said. This is rashness." Malik said, "The binding oath is for example, that a man says that he will not sell his garment for ten dinars, and then he sells it for that, or that he will beat his young slave and then does not beat him, and so on. One does kaffara for making such an oath, and there is no kaffara in rashness." Malik said, "As for the one who swears to a thing which he knows is wicked, and he swears to a lie he knows to be a lie, in order to please someone with it or to excuse himself to someone by it or to gain money by it, no kaffara that he does for it can cover it