Musannaf Ibn Abi Shaybah

Hazrat Urwah bin Ruwaym narrates that Hazrat Umar wrote a letter to Hazrat Abu Ubaidah bin Jarrah, which Hazrat Abu Ubaidah read out to the people in Jabiyah. It was written in it: From the servant of Allah, Umar, Ameer-ul-Mu'mineen, to Abu Ubaidah, peace be upon you. Only that person can enforce Allah's command among the people whose intellect is bright and whose strength is great, whose secrets people cannot discover, who does not become anxious in enforcing the truth, and who does not care about the blame of any blamer in the matter of Allah. Peace be upon you.