Musnad Ahmad 32:1423

Hashim narrated to us, Abd al-Aziz narrated to us, from Ishaq ibn Abdullah ibn Abi Talha, from Anas ibn Malik, who said: "The Messenger of Allah (peace and blessings of Allah be upon him) led us in prayer in the house of Umm Sulaym, upon a mat that had changed [in color] due to age. He sprinkled it with some water, and then he prostrated upon it."