Sunan An-Nasai, Chapter: The Book of Purification

(the freed slave of Ibn Abbas) that he heard him say: "Abdullah bin Yasar the freed slave of Maimunah, and I came and entered upon Abu juhaim bin Al-Harith bin Al-Sammah Al-Ansari. Abu Juhaim said: 'The Messenger of Allah (saw) came back from the direction of Bi'r Al-Jamal and was met by a man who greeted him with Salam, but the Messenger of Allah (saw) did not return the greeting until he turned to the wall and wiped his face and hands, then he returned the greeting.'" (Sahih)