Musannaf Ibn Abi Shayba 26:245

Waki’ narrated to us, he said: Sufyan narrated to us, from Mansur, from Ibrahim, who said: The Prophet (peace be upon him) fed three grandmothers. He said: I said to Ibrahim, "Who?" He said: "His paternal grandmother, the mother of his father, and his maternal grandmother, the mother of his mother."