Muawiyah who had already started negotiations with Hasan, sent high-level envoys, while committing himself in a witnessed letter to appoint Hasan his successor and give him whatever he wished. Hasan accepted the offer in principle and sent Amr ibn Salima al-Hamdani al-Arhabl and his own brother-in-law Muhammad ibn al-Ash'ath back to Muawiyah as his negotiators, together with the envoys of the latter. Muawiyah then wrote a letter saying that he was making peace with Hasan on the basis that Hasan would inherit the reign after him. He swore that he would not seek to harm him; and that he would give him 1,000,000 dirhams from the treasury (Bayt al-mal) annually, along with the land tax of Fasa and Darabjird; to which Hasan was to send his own tax agents to collect it. The letter was witnessed by the four envoys and dated in August 661.