Sahih Muslim

Sahih Muslim 1860 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
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Sahih Muslim 1860b
Arabic hadith text
وَحَدَّثَنَاهُ إِسْحَاقُ بْنُ إِبْرَاهِيمَ، حَدَّثَنَا حَمَّادُ بْنُ مَسْعَدَةَ، حَدَّثَنَا يَزِيدُ، عَنْ سَلَمَةَ، بِمِثْلِهِ
Translation

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