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