Khaybar in the seventh century was a prosperous Jewish settlement, its wealth built on dense date palms and a brisk trade in cloth, weapons, and luxury goods. It was not one town but a constellation of fortified redoubts scattered across the oasis, strongholds with names like al-Qamus, Na'im, and al-Watih, each defended by its own families. Among its people were the Banu Nadir, a Jewish tribe exiled from Medina a few years earlier who had settled here and, by the accounts that survive, worked to organize Arab tribes against the growing Muslim community. The fortresses held a siege-engine and stockpiles of arms. Whether kept for defense or for sale, they signaled a community that was wealthy, well-armed, and bracing for trouble.

The siege did not yield easily. The defenders, secure behind thick walls, kept to their fortresses and fought mostly with arrows at a distance, shifting people and treasure between strongholds under cover of darkness. The Muslims went hungry; supplies ran so short they were reduced to slaughtering captured donkeys. Two of Muhammad's most senior companions, Abu Bakr and then Umar, led assaults that failed. That night, the tradition holds, Muhammad declared that the next morning he would give the banner to a man who loved God and His Messenger, and whom God loved in return. The choice fell on Ali ibn Abi Talib, the Prophet's cousin and son-in-law, who had been laid up with an eye ailment. He took the flag and advanced on the fort, and the long stalemate finally broke.

At the gate of the citadel of al-Qamus, by the most famous account, Ali was met by Marhab, a Jewish champion renowned for his skill in battle. Marhab strode out chanting a boast of his own prowess, that Khaybar knew well he was a warrior tested, who thrust with the spear and struck with the sword. Ali answered, and in the exchange Marhab fell, killed by a single stroke. In one celebrated telling, Ali lost his shield in the fighting and tore a heavy door from the fortress to use in its place, a feat so prodigious that it became, for the Shi'a, the very image of the hero. Historians record the duel in different forms, but the core is consistent across the early sources: with Marhab's death, the defenders' resistance crumbled, and they sent word to negotiate.

The terms ended the fighting. The people of Khaybar surrendered their wealth, and those who wished to remain were allowed to keep working their orchards in exchange for handing over half their produce to the Muslims, an arrangement that let the oasis go on much as before. The human costs were real and personal. Among the captives was Safiyya, a young woman of seventeen, daughter of the slain Nadir chief and widow of the oasis treasurer Kenana; Muhammad offered her freedom, and she chose to convert and marry him, becoming one of the Mothers of the Believers. The early chronicles also preserve darker episodes, including the killing of Kenana over hidden treasure and a Jewish woman's attempt to poison Muhammad in revenge for her kin, accounts that some later Muslim scholars themselves questioned. The victory swelled Muhammad's standing and his army, and within eighteen months he would enter Mecca. The Jews of Khaybar lived on at the oasis until the caliph Umar expelled them years later.