Jami` at-Tirmidhi 3035

Narrated Abu Hurairah:that the Messenger of Allah (ﷺ) halted between Dajnan and 'Usfan, and the idolaters aid: "These people have a prayer which is more loved to them than their fathers and their children." That is, 'Asr. They gathered their forces and advanced altogether. And Jibra'il came to the Prophet (ﷺ) and told him to divide his Companions into two lines and lead them in prayer, and another group stood behind them on guard with their weapons. Then the other group came and prayed one Rak'ah with him. Then these people stood guard with their weapons, so each of them performed one Rak'ah while the Messenger of Allah (ﷺ) performed two Rak'ahs