Maliks Muwatta Book 22, Hadith Number 13.
Yahya related to me from Malik from Nafi that Abdullah ibn Umar used to do kaffara for a broken oath by feeding ten poor people. Each person got a mudd of wheat. He sometimes freed a slave if he had repeated the oath.
Yahya related to me from Malik from Yahya ibn Said that Sulayman ibn Yasar said, “I understood from people that when they made the kaffara for a broken oath, they gave a mudd of wheat according to the smaller mudd. They thought that that would compensate for them.”
Malik said, “The best of what I have heard about the one who does kaffara for breaking his oath by clothing people is that if he clothes men he clothes them each in one garment. If he clothes women, he clothes them each in two garments, a long shift and a long scarf, because that is what is satisfactory for each of them in the prayer.”