The early Islamic group was energized when, against overwhelming numbers, Muhammad’s military managed to kill approximately one thousand men from the Quraysh tribe, as historian Robert Spencer writes:
Muhammad heard that a large Quraysh caravan, laden with money and goods, was coming from Syria. “This is the Quraysh caravan containing their property,” he told his followers. “Go out and attack it, perhaps God will give it as a prey.” He set out toward Mecca to lead the raid. But this time the Quraysh were ready for him, coming out to meet Muhammad’s three hundred men with a force nearly a thousand strong. Muhammad seems not to have expected these numbers and cried out to Allah in anxiety, “O God, if this band perish today, Thou wilt be worshipped no more.”Despite their superior numbers, the Quraysh were routed. Some Muslim traditions say that Muhammad himself participated in the fighting, others that he exhorted his followers from the sidelines. In any event, it was an occasion for him to see years of frustration, resentment, and hatred toward his own people, who had rejected him, avenged. One of his followers later recalled a curse Muhammad had pronounced on the leaders of the Quraysh: “The prophet said, ‘O Allah! Destroy the chiefs of the Quraysh, O Allah!’”
Muhammed then listed aloud the names of the chiefs, one by one, who were to be killed. His followers listened and obeyed.
In addition to those who fell in battle, many were executed as prisoners. Robert Spencer gives names and details:
All the men were captured or killed during the battle of Badr. One Quraysh leader named in this curse, ‘Uqba, pleaded for his life, “But who will look after my children, O Muhammad?”“Hell,” responded the Prophet of Islam, and ordered ‘Uqba to be killed.
Another Quraysh chieftain, Abu Jahl (which means “Father of Ignorance,” a name given him by Muslim chroniclers; his real name was ‘Amr ibn Hisham) was beheaded. The Muslim who severed the head proudly carried his trophy to Muhammad: “I cut off his head and brought it to the apostle, saying, ‘This is the head of the enemy of God, Abu Jahl.’”
Muhammad was delighted. “By God than Whom there is no other, is it?” he exclaimed, and gave thanks to Allah for the death of his enemy.
From being a tiny, despised community, the Muslims were now a force with which the pagans of Arabia had to reckon - and they began to strike terror in the hearts of their enemies. Muhammad’s claim to be the last prophet of the One, True God appeared validated by a victory against enormous odds.
Islam grew and spread as various cities and tribes were defeated in battle; this encouraged the Muslims, and many of the non-Muslims in the area chose to convert to Islam rather than be killed in battle.