Zayd ibn Thabit · The Book of Fighting [The Prohibition of Bloodshed]

"The first matter concerning which scores will be settled among the people will be bloodshed."

"Jundab said: 'So and so told me that the Messenger of Allah said: The slain will bring his killer on the Day of Resurrection and will say: Ask him why he killed me. He will say: I killed him defending the kingdom of so and so.'" Jundab said: "So be careful.'"