It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the letter of the Messenger of Allah (peace and blessings be upon him) to the disbelievers was: "Come to a word that is equitable between us and you" [Surah Al Imran: 64], to the end of the verse.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12051