Musnad Ahmad 1153:766

Aswad ibn Amir narrated to us, he said: Isra'il narrated to us, from al-Mughirah, from Umm Musa, she said: I asked Aisha about the two rak'ahs after the afternoon prayer (Asr). She said: "The Prophet, peace and blessings of Allah be upon him, did not come to me on any day except that he prayed two rak'ahs after the afternoon prayer."