Musannaf Ibn Abi Shayba 3:5855

Yazid ibn Harun narrated to us, from Muhammad ibn Ishaq, from Hafs ibn Abdullah ibn Anas, who said: We used to travel with Anas ibn Malik. When the sun would pass its zenith while he was at a stopping place, he would not mount until he had prayed Dhuhr. If he departed and the time for Asr prayer arrived, and he had traveled from his stopping place before the sun passed its zenith and the prayer time arrived, we would say to him, "The prayer." He would say, "Travel on." Then, when it was between the two prayers, he would descend and combine the Dhuhr and Asr. Then he would say, "I saw the Messenger of Allah, peace and blessings of Allah be upon him, when he would join his late morning travel with his afternoon travel, he would do like this."