Sayyiduna Anas bin Malik (may Allah be pleased with him) says: The Prophet (peace and blessings of Allah be upon him) wrote a letter to Bakr bin Wa'il: "From Muhammad, the Messenger of Allah (peace and blessings of Allah be upon him) to Bakr bin Wa'il: Accept Islam and you will be safe." So this letter was read by a man from Banu Dubay'ah, whose name was Banu Katib.