Abu Dawud Book 19, Hadith Number 3652.
Chapter : Excellence of spreading knowledge.
Narated By Zayd ibn Thabit : I heard the Apostle of Allah (PBUH) say: May Allah brighten a man who hears a tradition from us, gets it by heart and passes it on to others. Many a bearer of knowledge conveys it to one who is more versed than he is; and many a bearer of knowledge is not versed in it.