Musnad Ahmad 1156:161

Ibn Numayr narrated to us, he said: Talhah ibn Yahya narrated to us, he said: Ubayd Allah ibn Abd Allah ibn Utbah claimed to me that Mu'awiyah sent to Aisha, asking her: "Did the Prophet, peace and blessings of Allah be upon him, pray anything after the Asr prayer?" She said: "As for me, no. But Umm Salamah informed me that he did that. So send to her and ask her." So he sent to Umm Salamah, and she said: "Yes, he entered upon me after the Asr prayer, and he prayed two prostrations (rak'ahs). I said: 'O Prophet of Allah, was something revealed to you regarding these two prostrations?' He said: 'No, but I prayed the Dhuhr prayer, then I was occupied, so I made it up after the Asr prayer.'"