Musnad Ahmad 1018:128

Hajjaj narrated to us, Shu'bah narrated to us, from Abu 'Imran, who said: I said to Jundub, "I have pledged allegiance to these people," meaning Ibn al-Zubayr, "and they want me to go out with them to al-Sham." He said, "Refrain." I said, "They refuse." He said, "Ransom yourself with your wealth." I said, "They refuse, except that I strike with the sword alongside them." Jundub said: So-and-so narrated to me that the Messenger of Allah (ﷺ) said: "The slain will come with his killer on the Day of Resurrection, and he will say: 'O Lord, ask this one why he killed me.'" Shu'bah said: And I think he said: "And He will say: 'For what did you kill him?' He said: 'He will say: I killed him for the kingdom of so-and-so.'" Jundub said: "So fear that."