Sunan Abi Dawud Book 4, Hadith 26
I accompanied Ibn 'Umar on the way (on a journey). He led us in two rak'ah's of (the noon) prayer. Then he proceeded and saw some people standing. He asked: What are they doing ? I replied: They are glorifying Allah (i.e. offering supererogatory prayer). He said: If I had offered the supererogatory prayer (while travelling), I would have completed prayer, my cousin. I accompanied the Messenger of Allah (ﷺ) during the journey, he did not pray more than two raka'at until his death. I also accompanied Abu Bakr, and he prayed two raka'at and nothing more until he died. I also accompanied 'Umar, and he prayed two raka'at and nothing more until he died. I also accompanied 'Uthman, and he prayed two raka'at and nothing more until he died. Indeed Allah, the Exalted, said: "Certainly you have in the Messenger of Allah an excellent exemplar"
I accompanied the Messenger of Allah (ﷺ) on eighteen journeys and I never saw him fail to pray two rak'ahs when the sun had passed the meridian before offering the noon prayer.
While travelling the Messenger of Allah (ﷺ) would pray voluntary prayer on his riding beast in whatever direction it turned; and he would observe witr prayer, but he did not offer the obligatory prayers upon it.