Musnad Ahmad 30:2643

Waki' narrated to us, he said: Ali ibn al-Mubarak narrated to us, from Yahya ibn Abi Kathir, from Abu Maymunah, from Abu Hurayrah: A woman came to the Prophet, may Allah bless him and grant him peace, whose husband had divorced her, and she wanted to take her child. The Messenger of Allah, may Allah bless him and grant him peace, said: "Draw lots for him." The man said: "Who will come between me and my son?" The Messenger of Allah, may Allah bless him and grant him peace, said to the son: "Choose whichever of the two you wish." So he chose his mother, and she went away with him.