Musnad Abu Ya'la al-Mawsili 3:70

Ubayd Allah narrated to us, Yazid bin Harun narrated to us, Muhammad bin Ishaq narrated to us, from Abu Ja'far Muhammad bin Ali, from his father, from his grandfather, who said: I found with the sword of the Messenger of Allah, may Allah bless him and grant him peace, a tied-up parchment [which read]: "The most hostile of people toward Allah is one who kills someone other than his killer, and one who strikes someone other than the one who struck him. And whoever denies the favor of his masters has disassociated himself from what Allah revealed to Muhammad, may Allah bless him and grant him peace."