Musannaf Ibn Abi Shaybah

It is narrated from Hazrat Hafs bin Ubaidullah bin Anas, he says that we used to travel towards Makkah with Hazrat Anas. So when the sun would decline and Hazrat Anas was staying at a place, he would not mount (his ride) before performing the Zuhr prayer. And when he would mount in the evening and the time for Asr was present, he would perform Asr. But if he had departed from his place before the sun's decline and the time for prayer arrived and we would say, "Prayer?" he would say: "Keep moving." Until when it was between the two prayers, he would dismount and combine Zuhr and Asr, and then say that I saw the Noble Prophet (peace and blessings be upon him) that when he would travel continuously from morning till evening, he would do likewise.