Sunan An-Nasai, Chapter: The Book of Leading the Prayer (Al-Imamah)

that he heard Abu Hurairah say: "The Iqamah for prayer was said, and we stood up and the rows were straightened, before the Messenger of Allah (saw) came out to us. Then the Messenger of Allah (saw) came to us and stood in the place where he prayed, before he said the Takbir he paused and said to us: 'Stay where you are.' So we stayed there, waiting for him, until he came out to us; he had performed Ghusl and his head was dripping with water. Then he said the Takbir and prayed." (Sahih)