Sunan at-Tirmidhi (Jami-al-Tirmidhi), Chapter: Salah (Prayers)

that his grand mother, Mulaykah, invited Allah's Messenger (SAW) to a meal prepared by her. He ate therefrom and then said, "Stand up, that we may pray with you." Anas said that he stood up and picked up his old mat which had turned black due to age. He sprinkled water on it and Allah's Messenger (SAW) stood on it and Anas and Yatim formed a row behind him. The old woman stood behind them. So, the Prophet prayed two rakaat with them, and then departed. [Ahmed 12342, Bukhari 380, Muslim 658, 612]