Abu Dawud Book 2, Hadith Number 1214.
Chapter : On the combination of two prayers at a time.
Narated By Anas b. Malik : When the Apostle of Allah (PBUH) proceeded before the sun had declined, he delayed the noon prayer till the time of the afternoon prayer; he would then alight and combine the two prayers. If the sun declined before he moved off, he would offer the noon prayer and rode (the beast) – PBUH.
Abu Dawud said: The narrator Mufaddal was the judge of Egypt. His supplication was accepted by Allah; he was the son of Fudalah.