Musannaf Ibn Abi Shayba 1:1046

1046. Isa ibn Yunus narrated to us, from al-A’mash, from Mujahid, who said: We were with Ibn Abbas on a journey, and he had a slave girl with him. He lagged behind and had intercourse with her, then he caught up with us. He said: "Do you have water with you?" We said: "No." He said: "I already knew that," and he performed tayammum.