Abdullah bin Umar (may Allah be pleased with them) narrates that the Prophet Muhammad (peace and blessings be upon him) received a letter from a man. The Prophet (peace and blessings be upon him) instructed Abdullah bin Arqam: "Reply on my behalf." He wrote the reply and read it to the Prophet (peace and blessings be upon him). The Prophet (peace and blessings be upon him) said: "You have written a very good reply. O Allah! Grant (Abdullah) success." When Umar bin Khattab (may Allah be pleased with him) became the caliph, he used to consult him.