Musannaf Ibn Abi Shayba 3:1450

Abu Bakr narrated to us, he said: Waki’ narrated to us, from ‘Isa ibn Hafs, from his father, he said: We went out with Ibn ‘Umar. He said: So we prayed the obligatory prayer, and he saw some of his children performing voluntary prayers. Ibn ‘Umar said: I prayed with the Messenger of Allah (peace and blessings of Allah be upon him), and Abu Bakr, and ‘Umar, and ‘Uthman, and there is no prayer before it nor after it during travel. And had I performed voluntary prayers, I would have completed [the prayer].