Abu Dawud Book 2, Hadith Number 1207.
Chapter : On the combination of two prayers at a time.
Narated By Ibn ‘Abbas : The Apostle of Allah (PBUH) combined the noon and the afternoon prayers, and the sunset and the night prayers at Medina without any danger or rain. He was asked: What did he intend by it? He replied: He intended that his community might not fall into hardship.