Abu Dawud Book 34, Hadith Number 4574.
Chapter : On a man who is killed blindly when the people are fighting with each other.
Narated By Abdullah ibn Abbas : The Prophet (PBUH) said: If anyone is killed blindly or, when people are throwing stones, by a stone or a whip, his blood-wit is the blood-wit for an accidental murder. But if anyone is killed intentionally, retaliation is due. If anyone tries to prevent it, the curse of Allah, of angels, and of all the people will rest on him.