Sayyiduna Anas bin Malik (may Allah be pleased with him) narrated that when the Messenger of Allah (peace and blessings be upon him) would set out on a journey before the sun had declined, he would not perform the Zuhr and Asr prayers until their time arrived, then he would stop somewhere (on the way) and combine Zuhr and Asr prayers. But if the sun had already declined before starting the journey, he would first perform the Zuhr prayer and then mount (his ride).