Sunan Ibn Majah, Chapter: The Chapters of Establishing the Prayer and the Sunnah Regarding Them

"Muawiyah sent word to Umm Salamah, and I went with his envoy who put the question to Umm Salamah. She said: 'While the Messenger of Allah (saw) was performing ablution for the Zuhr in my house and he had sent a Sa'i,* the Muhajirun gathered around him in large numbers, and he was busy dealing withthem. When a knock on the door came, he went out and performed the Zuhr, then he sat and distributed what had been brought to him.' She said: 'He continued doing that until the 'Asr. Then he came into my house and performed two Rakah. Then he said: "The matter of the Sa'i kept me from praying them after Zuhr, so I prayed them after 'Asr." Sahih