Musnad Ahmad 1156:206

Yazid narrated to us, he said: Hammad ibn Salamah informed us, from al-Azraq ibn Qays, from Dhakwan, from Umm Salamah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) prayed the Asr prayer, then he entered my house and prayed two rak'ahs. I said: "O Messenger of Allah, you have prayed a prayer that you did not used to pray." He said: "Some wealth came to me, and it distracted me from the two rak'ahs that I used to pray after the Dhuhr prayer, so I prayed them now." I said: "O Messenger of Allah, should we make them up if we miss them?" He said: "No."