Musnad Ahmad 30:3449

Yazid narrated to us, Hisham informed us, from Muhammad, from Abu Hurayrah, from the Prophet (peace and blessings of Allah be upon him), who said: "Sulayman ibn Dawud said: 'I will go around to one hundred women tonight, and each woman among them will give birth to a boy who will strike with the sword in the way of Allah.' But he did not make an exception (by saying 'if Allah wills')." He said: "So he went around to one hundred women that night, and none of them gave birth except for one woman, who gave birth to half a human." The Messenger of Allah (peace and blessings of Allah be upon him) said: "Had he said, 'If Allah wills,' every woman among them would have given birth to a boy who would strike with the sword in the way of Allah, the Mighty and Majestic."