Maliks Muwatta Book 20, Hadith Number 223.
Section : Stoning the Jamras.
Yahya related to me from Malik that he had heard some of the people of knowledge saying, “The pebbles used for stoning the jamras should be like the stones used as slingshot.”
Malik said, “I like it better if they are a little larger than that.”
Yahya related to me from Malik from Nafi that Abdullah ibn Umar used to say, “Someone who is at Mina when the sun sets in the middle of the days of tashriq must not leave until he has stoned the jamras on the following day.”