Sahih Muslim
The Book of Prayers (Kitab Al-Salat)
Book Number: 004 / Hadith Number: 1545
Ka'b b. Malik reported: The Messenger of Allah (may peace be upon him) did not come back from the journey but by day in the forenoon, and when he arrived, he went first to the mosque, and having prayed two rak'ahs in it he sat down in it.