Sahih Bukhari Volume 3, Book 47, Hadith 2491

حَدَّثَنَا أَبُو الْوَلِيدِ، حَدَّثَنَا شُعْبَةُ، عَنْ جَبَلَةَ، قَالَ كُنَّا بِالْمَدِينَةِ فَأَصَابَتْنَا سَنَةٌ، فَكَانَ ابْنُ الزُّبَيْرِ يَرْزُقُنَا التَّمْرَ، وَكَانَ ابْنُ عُمَرَ يَمُرُّ بِنَا فَيَقُولُ لاَ تَقْرُنُوا فَإِنَّ النَّبِيَّ صلى الله عليه وسلم نَهَى عَنِ الإِقْرَانِ، إِلاَّ أَنْ يَسْتَأْذِنَ الرَّجُلُ مِنْكُمْ أَخَاهُ‏

Narrated By Jabala : "While at Medina we were struck with famine. Ibn Az-Zubair used to provide us with dates as our food. Ibn 'Umar used to pass by us and say, "Don't eat two dates together at a time as the Prophet has forbidden eating two dates together at a time (in a gathering) unless one takes the permission of one's companion brother."