Musnad Ahmad 32:400

I read to Abd al-Rahman: Malik, 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. He ate from it, then the Messenger of Allah, may Allah bless him and grant him peace, 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 long use, 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 stood behind us. The Messenger of Allah, may Allah bless him and grant him peace, led us in two rak'ahs of prayer, then he departed.