The Book of Drinks (Kitab Al-Ashriba)
Muslim :: Book 23 : Hadith 5075
Jabala b. Suhaim reported: Ibn Zubair used to provide us with dates during the time that the people were hard pressed because of famine (Once) as we were busy in eating there happened to appear before us Ibn 'Umar. He said: Don't eat two dates together, for Allah's Messenger (may peace be upon him) forbade eating them together but only after seeking permission from his brother (partner). Shu'ba said: I do not think these words pertaining to seeking permission but from the words of Ibn 'Urnar.