Abu Dawud Book 019, Hadith Number 3639.

Chapter : Writing the knowledge.

Narated By Abdullah ibn Amr ibn al-'As : I used to write everything which I heard from the Apostle of Allah (pbuh). I intended (by it) to memorise it. The Quraysh prohibited me saying: Do you write everything that you hear from him while the Apostle of Allah (pbuh) is a human being: he speaks in anger and pleasure? So I stopped writing, and mentioned it to the Apostle of Allah (pbuh). He signalled with his finger to him mouth and said: Write, by Him in Whose hand my soul lies, only right comes out from it.