Musnad Ahmad 30:1346

Ya'qub narrated to us, my father narrated to us, from Salih, from Ibn Shihab, Abu Salamah ibn 'Abd al-Rahman narrated to me, that Abu Hurayrah said: The Messenger of Allah (peace and blessings of Allah be upon him) went out when the prayer had been established and the rows had been straightened. When he stood in his place of prayer and we were waiting for him to say the Takbir, he turned away and said: "Stay in your places." He entered his house, and we remained in our state until he came out to us, with his head dripping, having performed ghusl.