Ibn Dhi al-Kala' narrates: (A letter) came to Sayyiduna Mu'awiyah (may Allah be pleased with him) from the governor of Armenia. When Sayyiduna Mu'awiyah (may Allah be pleased with him) read the letter, he came out in anger, then called his scribe and said: Write to the governor of Armenia in reply to his letter: May your mother be bereaved of you! Do not provoke them in any way, for I heard the Messenger of Allah (peace and blessings be upon him) say: "Leave the Turks alone as long as they leave you alone."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 16932