Musnad Ahmad 572:17

'Affan narrated to us, he said: Hammad ibn Salamah narrated to us, from Humayd, from al-Hasan, from 'Uthman ibn Abi al-'As, that the delegation of Thaqif came to the Messenger of Allah, may Allah bless him and grant him peace. He lodged them in the mosque so that it would be softer for their hearts. They stipulated to the Prophet, may Allah bless him and grant him peace, that they would not be gathered (for military service), nor would they be taxed (tithed), nor would they pay the jizyah, and that no one other than them would be appointed over them. He said: So he said: "You shall have that you will not be gathered, nor will you be taxed, and no one other than you will be appointed over you." And the Prophet, may Allah bless him and grant him peace, said: "There is no good in a religion in which there is no bowing." He said: And 'Uthman ibn Abi al-'As said: "O Messenger of Allah, teach me the Qur'an, and make me the leader of my people."