Musnad Ahmad Hadith 10765

It is narrated from Abu Huraira (may Allah be pleased with him) that once the Noble Prophet (ﷺ) camped between Dajnan and Usfan. The polytheists consulted among themselves, saying, "Their Asr prayer is more beloved to them than their forefathers and their wives, so gather together and attack them at that time so that they may be defeated all at once." Meanwhile, Jibreel (peace be upon him) came to the service of the Noble Prophet (ﷺ) and instructed the Prophet (ﷺ) to arrange his companions (may Allah be pleased with them) into two groups, so that the Prophet (ﷺ) could lead one group in prayer while the other stood facing the enemy, keeping their protective gear and weapons with them. Then the second group would come and pray with the Noble Prophet (ﷺ), while the first group would keep their protective gear and weapons with them. In this way, each group would perform one rak'ah with the Noble Prophet (ﷺ), and the Prophet (ﷺ) would complete both rak'ahs.