From Sahih Muslim (Hadith 1632):
Mu'adh b. Jabal reported: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
Reference: Muslim 1632