Sahih Muslim Book 6, Hadith 55
I saw the Messenger of Allah (ﷺ) delaying the sunset prayer till he would combine it with the 'Isha' when he hastened to set out on a journey.
I saw the Messenger of Allah (ﷺ) combining the sunset and Isha' prayers when he was in a hurry on a journey.
When the Messenger of Allah (ﷺ) set out on a journey before the sun declined (from the meridian), he delayed the noon prayer till the afternoon prayer, and then dismounted (his ride) and combined them (noon and afternoon prayers), but if the sun had declined before his setting out on a journey, he observed the noon prayer and then mounted (the ride).