Sahih Muslim 1860b

(18) – باب اسْتِحْبَابِ مُبَايَعَةِ الإِمَامِ الْجَيْشَ عِنْدَ إِرَادَةِ الْقِتَالِ وَبَيَانِ بَيْعَةِ الرِّضْوَانِ تَحْتَ الشَّجَرَةِ

(18) – 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

The above tradition has also been handed down through a different chain of transmitters.

وَحَدَّثَنَاهُ إِسْحَاقُ بْنُ إِبْرَاهِيمَ، حَدَّثَنَا حَمَّادُ بْنُ مَسْعَدَةَ، حَدَّثَنَا يَزِيدُ، عَنْ سَلَمَةَ، بِمِثْلِهِ .

Sahih (Authentic)