The Book on Government
33/18. Chapter:
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
Sahih Muslim
وَحَدَّثَنَا ابْنُ الْمُثَنَّى، حَدَّثَنَا أَبُو دَاوُدَ، ح وَحَدَّثَنَاهُ إِسْحَاقُ بْنُ إِبْرَاهِيمَ، أَخْبَرَنَا النَّضْرُ بْنُ شُمَيْلٍ، جَمِيعًا عَنْ شُعْبَةَ، بِهَذَا الإِسْنَادِ مِثْلَهُ .
The same tradition has been handed down through a different chain of transmitters.
Reference : Sahih Muslim 1857bIn-book reference : Book 33, Hadith 113USC-MSA web (English) reference : Book 20, Hadith 4585