Sa'd ibn Mu'adh (Arabic: سعد ابن معاذ) (c.591-627) was the chief of the Aws tribe in Medina and one of the prominent companions of the Islamic prophet Muhammad. He died shortly after the Battle of the Trench.
Sa'd was born in Medina c.591, the son of Mu'adh ibn al-Numan, of the Abdul-Ashhal clan of the Aws tribe, and of Kabsha bint Rafi, of the al-Harith clan of the Khazraj tribe.
He married Hind bint Simak, his agnatic second cousin, whose brother had been chief of the Aws tribe until he was killed at the Battle of Bu'ath. They had two sons, Amr and Abdullah.
As'ad ibn Zurarah, chief of the al-Najjar clan of the Khazraj, was Sa'd's maternal first cousin. Usayd ibn Hudayr was his wife's fraternal nephew, and was also said by al-Waqidi to have been Sa'd's first cousin.
Sa'd adopted Islam in 622 (1 AH), when Muhammad arrived in Medina, then known as Yathrib. He was among the leading figures among the Ansar, as Muhammad had dubbed the people of Aws and Khazraj from Medina who converted to Islam.
Sa'd was an intimate friend of Umayah ibn Khalaf. When Sa'd was in Mecca, he used to stay with Umayah, and when Umayah was in Medina, he used to stay with Sa'd.
Prior to the Battle of Badr, Sa’d had visited Mecca once to perform his Umra with his non-Muslim friend Umayah ibn Khalaf, when they came across Abu Jahl. They had an argument, and as it became heated, Sa'd threatened Abu Jahl with preventing his safe passage through Medina if he stopped the Muslims from performing pilgrimage in Mecca. Narrated 'Abdullah bin Mas'ud: