Musnad Ahmad 32:565

Ishaq ibn Isa—meaning al-Taba’—narrated to us, Malik narrated to us, from Ishaq ibn Abdullah ibn Abi Talha, from Anas ibn Malik, that his grandmother, Mulaykah, invited the Messenger of Allah (may Allah bless him and grant him peace) for food she had prepared. The Messenger of Allah (may Allah bless him and grant him peace) ate from it, then said: "Stand up, so that I may lead you in prayer." Anas said: I stood up to a mat of ours that had turned black from the length of time it had remained, and I sprinkled it with water. The Messenger of Allah (may Allah bless him and grant him peace) stood upon it, and I and the orphan stood behind him, and the old woman was behind us. He prayed two rak'ahs with us, then departed.