Community relationships In the early period after Muhammad's arrival, Sa'd urged the Jews of Medina to accept Islam. "Fear God," he said, "for you know right well that [Muhammad] is God's Messenger, of whom you used to speak to us before his mission and describe him to us." The Jews replied: "We never said that to you, and
God has sent down no book since
Moses nor sent an evangelist or warner after him." Saad's son Qays was among 300 men who were sent under
Abu Ubayda ibn al-Jarrah against the
Juhayna tribe in October 629. There was no food and the men were hungry. Qays began to buy camels on his father's credit to slaughter for the army. After three days of this, Abu Ubayda stopped him, saying that he must not spend his father's money without permission. Umar supported Abu Ubayda's argument, and Qays was "most rude" to Umar. When Sa'd heard about the army's hunger, he said: "If I know Qays, he will slaughter for the people!" When Qays returned and told him the story of how Abu Ubayda had halted his spending, Sa'd immediately gave his son four date-orchards so that in future he would have money that was legally his own. Then he paid off the debts. Sa'd was one of those who laid the corpse of Abdullah ibn Ubayy at his burial.
The accusation against Aisha Abdullah ibn Ubayy encouraged rumours that Muhammad's wife
Aisha had committed adultery. Muhammad addressed the Muslims in the mosque about it: "Why do certain men lie about my family?" An Aws leader, Usayd ibn Hudayr, replied: "If they are of Aws let us rid you of them; and if they are of the Khazraj give us your orders, for they ought to have their heads cut off." Sa'd ibn Ubadah stood up and retorted: "By Allah, you lie. They shall not be beheaded. You would not have said this if you had not known that they were of Khazraj. If they had been your own people, you would not have said it." Sa'd's words triggered a loud quarrel in the mosque. Usayd ibn Hudayr retorted, "Liar yourself! We would certainly kill him, despite your efforts. You are a hypocrite who defends hypocrites! By God, if the Messenger desired the head of my closest relative, I would bring it to him before he could stand up. But I don’t know what the Messenger wants." Sa'ad told him: "You Aws insist on treating us with the resentment that was between us in the
Jahiliya. By God, there is no need to remember it. Surely you know who was victorious in it. Indeed, God extinguished all of that with Islam." Usayd stood up and said, "You saw our stand at the
Battle of Bu'ath!" At this Sa'd was so angry that he called out: "O Sons of Khazraj!" and all the Khazraj came to stand on his side. Sa'd ibn Mu'adh called out, "O Sons of Aws!" and the Aws went to stand next to him. With the two tribes lined up, a Khazraj man unsheathed a sword, announcing, "I will cut off the head of the hypocrite in his hideout!" Usayd met him and said: "Drop it! A weapon is brought out only by the command of Allah's Messenger. If we knew that the Messenger had such a desire or command, then we would do this faster than you." Muhammad called for silence, stepped down from the pulpit and managed to calm them down. The accused man,
Safwan ibn Mu'attal, attacked one of the slanderers,
Hassan ibn Thabit. Hassan's friends captured Safwan, tied him up and kept him in prison. Sa'd made peace between them. He persuaded Hassan's friends to release Safwan and to drop their blood-claim against him; then he gave Safwan new clothes. He then compensated Hassan for the sword-cut by giving him a valuable palm-tree garden. ==Military career under Muhammad==