Conversion Through Mus’ab
Mus’ab ibn Umayr, sent to Medina before the Hijra to teach the new Muslims, worked among the Aws and Khazraj tribes. When he approached the Banu Aws, the chieftain was Saad ibn Muadh. Saad initially sent a hostile emissary to stop Mus’ab — but when he spoke with Mus’ab and heard the Quran, he converted. As chief, his conversion had an immediate cascading effect among his tribe.
The Arbitration of Banu Qurayza
After the Battle of the Trench, Banu Qurayza, who had violated their treaty with the Muslims, surrendered. Both the Banu Aws (their traditional allies) and the Muslims asked the Prophet to let Saad ibn Muadh arbitrate — as chief of Banu Qurayza’s former allies, his judgment would be both trusted and binding.
Saad was brought to the judgment seat on a donkey, barely able to sit because of his wound. He asked three times: “Do you agree to accept my arbitration?” Both parties agreed. His judgment: the fighting men would be executed, the women and children enslaved, and property distributed.
The Prophet affirmed: “You have judged according to the judgment of God."
"The Throne Shook”
The hadith in Bukhari (3803): “The throne of the Merciful (‘arsh al-Rahman) shook for the death of Saad ibn Muadh.” The scholarly discussions about this hadith range from literal (the divine throne expressed a cosmic response) to metaphorical (the angels rejoiced with a movement like the throne trembling).
See also: Seerah Nuaym Ibn Masud Al Ashjai, Seerah Jabir Ibn Samurah, Seerah Khandaq, Seerah Al Miswar Ibn Makhrama, Seerah Zaid Ibn Arqam