Musannaf Ibn Abi Shaybah

It is narrated from Hazrat Abu Majliz that Hazrat Umar Farooq sent Hazrat Usman bin Hunaif (to collect ‘ushr and other dues). He fixed one dirham on every twenty dirhams for the dhimmis whose wealth had been transferred to other cities and who engaged in trade, and he wrote this to Hazrat Umar Farooq. He was pleased with this and granted permission for it. Then Hazrat Umar Farooq was asked: What do you command us regarding how much we should collect from the traders of the people at war (ahl al-harb)? He replied: When you go to their cities, how much do they collect from you? The people said: ‘Ushr (a tenth). So he said: Then you should collect the same from them.