Hadith 119

Sahih Muslim

Book 33: The Book on Government

Chapter 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

باب اسْتِحْبَابِ مُبَايَعَةِ الإِمَامِ الْجَيْشَ عِنْدَ إِرَادَةِ الْقِتَالِ وَبَيَانِ بَيْعَةِ الرِّضْوَانِ تَحْتَ الشَّجَرَةِ

Sahih Muslim 1860b
وَحَدَّثَنَاهُ إِسْحَاقُ بْنُ إِبْرَاهِيمَ، حَدَّثَنَا حَمَّادُ بْنُ مَسْعَدَةَ، حَدَّثَنَا يَزِيدُ، عَنْ سَلَمَةَ، بِمِثْلِهِ ‏.‏
The above tradition has also been handed down through a different chain of transmitters.