(523) بَابُ جَوَابِ الْكِتَابِ
Ibn 'Abbas said, "I think that answering a letter is a duty, justlike returning the greeting." (JA)
Reference (JA): Al-Adab Al-Mufrad 1117 (JA)
In-book reference (JA): Book 45, Hadith 1 (JA)
English translation (JA): Book 45, Hadith 1117 (JA)