From Sahih Bukhari (Hadith 2490):
Narrated 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 (ﷺ) has forbidden eating two dates together at a time (in a gathering) unless one takes the permission of one's companion brother
Reference: Bukhari 2490