Sahih Adab al-Mufrad

784/1023- (Authentic chain of narration) From Ibn Shihab: That Umar ibn Abd al-Aziz asked Abu Bakr ibn Sulayman ibn Abi Hathmah: Why did Abu Bakr write: From Abu Bakr; the Caliph of the Messenger of Allah. Then after him, Umar wrote: From Umar ibn al-Khattab; the Caliph of Abu Bakr. Who was the first to write: Commander of the Believers (Amir al-Mu'minin)? He said: My grandmother al-Shifa’ told me—and she was among the first emigrant women, and Umar ibn al-Khattab, may Allah be pleased with him, whenever he entered the market, he would enter upon her—she said: "Umar ibn al-Khattab wrote to the governor of the two Iraqs: Send me two strong and noble men; I want to ask them about Iraq and its people. So the governor of the two Iraqs sent him Labid ibn Rabi‘ah and ‘Adi ibn Hatim. They arrived in Medina, tied their mounts in the courtyard of the mosque, then entered the mosque and found ‘Amr ibn al-‘As. They said to him: O ‘Amr! Seek permission for us to enter upon the Commander of the Believers; Umar. So ‘Amr jumped up and entered upon Umar. He said: Peace be upon you, O Commander of the Believers! Umar said: What made you use this title, O son of al-‘As? You must explain what you said. He said: Yes, Labid ibn Rabi‘ah and ‘Adi ibn Hatim arrived and said to me: Seek permission for us to enter upon the Commander of the Believers. I said: By Allah, you have named him rightly, for he is the commander, and we are the believers. So from that day, the title was used in correspondence."