Sahih Muslim
Sahih Muslim 1856 b
It is recommended for the army to swear allegiance to the ruler when intending to fight, and an account of Bay'at Ar-Ridwan beneath the tree
Arabic hadith text
وَحَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا ابْنُ عُيَيْنَةَ، ح وَحَدَّثَنَا ابْنُ نُمَيْرٍ، حَدَّثَنَا سُفْيَانُ، عَنْ أَبِي الزُّبَيْرِ، عَنْ جَابِرٍ، قَالَ لَمْ نُبَايِعْ رَسُولَ اللَّهِ صلى الله عليه وسلم عَلَى الْمَوْتِ إِنَّمَابَايَعْنَاهُ عَلَى أَنْ لاَ نَفِرَّ .
Translation
It has been narrated (through a different chain of transmitters) on the authority of Jabir who said
While swearing fealty to the Prophet (ﷺ) we did not take the oath to death but that we would not run away (from the battlefield).