Mishkatul Masabih — Hadith #40157

He said, the Prophet (peace and blessings of Allah be upon him) during the battle of Tabuk, when the sun went down at the time of Zuhr, he would delay the Zuhr and 'Asr prayers, and he would go down to the floor for the 'Asr prayer, that is, he would perform the Zuhr and 'Asr prayers together. Maghrib prayer He used to do the same. If the sun set before his return, he (may peace be upon him) would offer the Maghrib and 'Isha prayers together. And if the sun left before sunset, he (may peace be upon him) would delay the Maghrib prayer. He used to go down for the 'Isha' prayer and offer two prayers together. (Abu Dawud, Tirmidhi) [1]