Maliks Muwatta Book 38, Hadith Number 24.
Section : The Inheritance of the Wala’.
Malik related to me that he had heard that Said ibn al-Musayyab spoke about a man who died and left three sons and left mawali whom he had freed. Then two of his sons died and left children. He said, “The third remaining son inherits the mawali. When he dies, his children and the children of his brothers share equally in the wala’ of the mawali.”