His grandmother Mulaykah invited the Messenger of Allah ﷺ to a meal she had prepared. He ate some of it and then said, "Get up so I may lead you in prayer."Anas said, "I went to a straw mat of ours that had turned black from long use and sprinkled it with water. The Messenger of Allah ﷺ stood on it, and the orphan and I lined up behind him, with the old woman behind us. He led us in two units of prayer and then left."
حدثنا إسحق الأنصاري حدثنا معن حدثنا مالك بن أنس عن إسحق بن عبد الله بن أبي طلحة
أن جدته مليكة دعت رسول الله ﷺ لطعام صنعته فأكل منه ثم قال قوموا فلنصل بكم قال أنس فقمت إلى حصير لنا قد اسود من طول ما لبس فنضحته بالماء فقام عليه رسول الله ﷺ وصففت عليه أنا واليتيم وراءه والعجوز من ورائنا فصلى بنا ركعتين ثم انصرف
Both Bukhari and Muslim included this. Bukhari transmitted it in the Book of Prayer, chapter on praying on a mat, hadith no. 380, and Muslim in the Book of Mosques, chapter on the permissibility of congregational prayer in supererogatory prayers, etc., hadith no. 658, both from the hadith of Malik through this same route, and it is found in Muwatta (Yahya's version) 1/153.