Musnad Ahmad 1153:769

Aswad ibn Amir narrated to us, he said: Isra'il narrated to us, from al-Miqdam ibn Shurayh, from his father, who said: I said to Aisha: "What did the Messenger of Allah, peace and blessings of Allah be upon him, do before he would go out?" She said: "He would pray the two rak'ahs, then he would go out."