"The Prophet only performed the two rak'ah (units of prayer) after Asr because some wealth came to him which distracted him from the two rak'ah after Zuhr, so he prayed them after Asr, then he did not repeat that."

“Determined to contemplate the ritual prayer of the Prophet (Allah bless him and give him peace) intently, for I laid my head on his doorstep or [the entrance to] his hair tent. Allah’s Messenger (Allah bless him and give him peace) then performed two brisk cycles of ritual prayer. After this he performed two long, long, long cycles. Then he performed two cycles that were shorter than the two before them. Then he performed two cycles that were shorter than the two that were before them. Then he performed two cycles that were shorter than the two that preceded them. Then he performed two cycles that were shorter than the two that were before them. Finally he performed a single-numbered cycle, which added up to a total of thirteen cycles.”