Ubaidullah bin 'Umar bin Hafs عبيد الله بن عمر بن حفص بن عاصم · The Book on Traveling

"I traveled with the Prophet, Abu Bakr, Umar, and Uthman; they would pray Zuhr and Asr as two Rak'ah and two Rak'ah, not praying before them nor after them." And Ibn Umar said: "If I was going to pray before it or after it then I would pray it complete."

"Ibn Umar had been requested to urgently attend to one of his wives, so he hurried en route and delayed Maghrib until the twilight disappeared, then he dismounted to combine them (the prayers). Then he informed them that the Messenger of Allah would do that when he was in a hurry on a trip."