Musannaf Ibn Abi Shaybah

Hazrat Ubaidullah bin Abdullah narrates that Hazrat Umar Farooq appointed my father and another person as officials to collect charity (such as ushr, etc.) from the dhimmis who had moved to different cities and were doing business there, and he instructed us to collect half of ushr from them on wheat as a concession so that they could bring it to the city, and to collect full ushr on lentils and other such items.