Amr bin Yahya al-Mazini narrates from his father that the Messenger of Allah (peace and blessings be upon him) said: "Do not cause harm, and do not suffer harm."
This is mursal, and we have narrated it with a connected chain in the Book of Reconciliation (Kitab al-Sulh).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب آداب القاضي / 20444