Sahih Bukhari Volume 7, Book 65, Hadith Number 357.

Narrated By Jabala bin Suhaim : At the time of Ibn Az-Zubair, we were struck with famine, and he provided us with dates for our food. ‘Abdullah bin ‘Umar used to pass by us while we were eating, and say, “Do not eat two dates together at a time, for the Prophet forbade the taking of two dates together at a time (in a gathering).” Ibn ‘Umar used to add, “Unless one takes the permission of one’s companions.”