Abd al-Wahid bin Abi Awn (may Allah have mercy on him) narrates: A man's letter came to the Prophet (peace and blessings be upon him), and he (peace and blessings be upon him) said to Sayyiduna Abdullah bin al-Arqam (may Allah be pleased with him): "Write a reply on my behalf." So he wrote the reply, then read it out to him (peace and blessings be upon him), and he (peace and blessings be upon him) said: "You have written correctly and well. O Allah, grant him success." Then, when Sayyiduna Umar (may Allah be pleased with him) became caliph, he used to consult him.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14048