Muawiyah, who had already started negotiations with Al-Hasan, now 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 al-Kindi back to Mu'awiyah as his negotiators, along with Muawiyah's envoys. Mu'awiyah then wrote a letter saying that he was making peace with Hasan, who would become caliph 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, which Hasan was to send his own tax agents to collect. The letter was witnessed by the four envoys and dated in August 661.