Musannaf Ibn Abi Shayba 1:615

Abdullah ibn Idris narrated to us, from Muhammad ibn Ammarah, from Muhammad ibn Ibrahim, from an Umm Walad of Abd al-Rahman ibn Awf, who said: I used to lengthen my hem, and I would pass by dirty places and clean places. So I entered upon Umm Salamah and asked her. Umm Salamah said: I heard the Messenger of Allah (ﷺ) say: "What comes after it purifies it."