Musnad Ahmad 967:1

Muhammad ibn Isma'il ibn Abi Fudayk narrated to us, al-Dahhak ibn 'Abd Allah narrated to us, from the one who narrated to him, from 'Amr ibn 'Abd Allah ibn Ka'b, from a woman among those who gave the pledge of allegiance, that she said: The Messenger of Allah (peace and blessings of Allah be upon him) came to us with his companions in Banu Salamah. We brought food near to him, and he ate, and his companions were with him. Then we brought water for ablution near to him, and he performed ablution. Then he turned to his companions and said: "Shall I not inform you of the things that expiate sins?" They said: "Yes." He said: "Performing ablution thoroughly despite difficulties, taking many steps to the mosques, and waiting for the prayer after the prayer."