Sahih Bukhari Volume 9, Book 95, Hadith 7258

حَدَّثَنَا سُلَيْمَانُ بْنُ حَرْبٍ، حَدَّثَنَا حَمَّادُ بْنُ زَيْدٍ، عَنْ يَحْيَى بْنِ سَعِيدٍ، عَنْ عُبَيْدِ بْنِ حُنَيْنٍ، عَنِ ابْنِ عَبَّاسٍ، عَنْ عُمَرَ ـ رضى الله عنهم ـ قَالَ وَكَانَ رَجُلٌ مِنَ الأَنْصَارِ إِذَا غَابَ عَنْ رَسُولِ اللَّهِ صلى الله عليه وسلم وَشَهِدْتُهُ أَتَيْتُهُ بِمَا يَكُونُ مِنْ رَسُولِ اللَّهِ صلى الله عليه وسلم وَإِذَا غِبْتُ عَنْ رَسُولِ اللَّهِ صلى الله عليه وسلم وَشَهِدَ أَتَانِي بِمَا يَكُونُ مِنْ رَسُولِ اللَّهِ صلى الله عليه وسلم‏

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.