Sahih Bukhari Volume 009, Book 091, Hadith Number 362.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 91. Accepting Information given by a Truthful Person
Narrated By 'Umar : There was a man from the Ansar (who was a friend of mine). If he was not present in the company of Allah's Apostle I used to be present with Allah's Apostle, I would tell him what I used to hear from Allah's Apostle, and when I was absent from Allah's Apostle he used to be present with him, and he would tell me what he used to hear from Allah's Apostle.