It was narrated from Ibn 'Abbas that the Prophet (ﷺ) used to pray in Al-Madinah combining two prayer. Joining Zuhr and 'Asr, and Maghrib and 'Isha', when there was no fear nor rain. It was said to him:
"Why?" He said: "So that there would not be any hardship on his Ummah." (DE)
English reference (DE): Vol. 1, Book 6, Hadith 603 (DE)
Arabic reference (DE): Book 6, Hadith 609 (DE)