Amr bin Yahya al-Mazini (may Allah have mercy on him) narrates from his father that the Messenger of Allah (peace and blessings be upon him) said: "La darar wa la dirar: do not cause harm, and do not harm anyone in retaliation."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب إحياء الموات / 11878