Musnad Ahmad 1007:78

Sufyan narrated to us, from Uthman ibn Abi Sulayman, who heard Amir ibn Abdullah ibn al-Zubayr narrating, from Amr ibn Sulaym, from Abu Qatadah, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "When one of you enters the mosque, let him pray two rak'ahs before he sits down." Abdullah said: And my father said: And he narrated to us another time, and said: From Uthman ibn Abi Sulayman ibn Ajlan, from Amir ibn Abdullah ibn al-Zubayr, and he mentioned the hadith.