Musannaf Ibn Abi Shayba 13:2848

Abu Bakr narrated to us, he said: Hafs narrated to us, from Ibn Abi Layla, from al-Hakam, from Ali, he said: The Prophet, may Allah bless him and grant him peace, sent me with two young male captives, who were slaves, for me to sell them. When I came to him, he said: "Did you join [them] or did you separate [them]?" I said: "I separated [them]." He said: "Then overtake [them], overtake [them]."