Musannaf Ibn Abi Shaybah

It is narrated from Hazrat Abu Uthman. He says that Hazrat Umar wrote a letter to Hazrat Abu Musa: "Cut the stirrups of the horses and ride them gently, wear shoes and take off the socks, wear waistcloths instead of trousers, shoot arrows at the target, wear rough and coarse clothes, do not adopt the luxury and comfort of the non-Arabs, for the way of the non-Arabs is the worst way."