Musannaf Ibn Abi Shayba 18:1215

Abu Bakr narrated to us, he said: Waki' narrated to us, from Sufyan, from Alqama bin Marthad, from Sulayman bin Burayda, from his father, who said: When the Messenger of Allah (peace and blessings of Allah be upon him) would send out a military expedition, he would say: "Do not mutilate."