Musnad Abu Ya'la al-Mawsili 3:60

Ubayd Allah narrated to us, Yazid bin Zuray' and Abdullah bin Dawud narrated to us, from Sufyan, from Abd al-A'la, from Abu Jamilah, from Ali, who said: The Messenger of Allah (peace and blessings of Allah be upon him) sent me to a slave girl who had committed adultery, and he said: "Carry out the prescribed punishment upon her." I found her in her blood, not having recovered from her postpartum bleeding. I came to him and mentioned that to him, and he said: "When she has recovered from her postpartum bleeding and has become pure, then carry out the prescribed punishment upon her." He said: Then he said: "Carry out the prescribed punishment upon those whom your right hands possess."