Sahih Muslim
The Book of Prayers (Kitab Al-Salat)
Book Number: 004 / Hadith Number: 1387
Anas b. Malik reported that his grandmother, Mulaika, invited the Messenger of Allah (may peace be upon him) to a dinner which she had prepared. He (the Holy Prophet) ate out of that and then said: Stand up so that I should observe prayer (in order to bless) you Anas b. Malik said: I stood up on a mat (belonging to us) which had turned dark on account of its long use. I sprinkled water over it (in order to soften it), and the Messenger of Allah (may peace be upon him) stood upon it, and I and an orphan formed a row behind him (the Holy Prophet) and the old woman was behind us, and the Messenger of Allah (may peace be upon him) led us in two rak'ahs of prayer and then went back.