A man hosted some people from Hudhayl. They sent a slave woman to fetch some firewood, and the host was attracted to her, so he followed her and wanted to have his way with her, but she refused.
He wrestled with her for a while, then she escaped from him and threw a rock at him and killed him. Then she came to her masters and told them what had happened (loyalty!).
Her masters went to ‘Umar (who was the khaleefah at the time) and told him, and ‘Umar sent investigators who found their tracks.
‘Umar said, “No diyah (blood-money paid by the assassin) is to be paid for one who was killed by Allaah.“
He regarded it as legitimate to have shed the blood of that aggressor, so there was to be no qisaas (retaliation) or diyah, and no expiation was to be offered.
[Taken from: ‘Umar Ibn Al-Khattaab His Life And Times, by Dr. ‘Alee Muhammad As-Sallaabi, p. 527]