It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "The most hateful of people to Allah is one who seeks the way of Jahiliyyah in Islam, and one who seeks a person's blood unjustly in order to shed his blood."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10703