Sahih Muslim Book 6, Hadith 62
We set out with the Messenger of Allah (ﷺ) on the Tabuk expedition, and he observed the noon and afternoon prayers together and the sunset and 'Isha' prayers together.
What prompted him to do this? He said: He wanted that his Ummah should not be put to (unnecessary) hardship.
The Messenger of Allah (ﷺ) combined in the expedition to Tabuk the noon prayer with the afternoon prayer and the sunset prayer with the 'Isha' prayer. He (one of the narrators) said: What prompted him to do that? He (Mu'adh) replied that he (the Holy Prophet) wanted that his Ummah should not be put to (unnecessary) hardship.