Hadith 741
Jabalah bin Suhaim reported:
عن جبلة بن سحيم قال: أصابنا عام سنةٍ مع ابن الزبير، فرزقنا تمراً، وكان عبد الله بن عمر رضى الله عنهما يمر بنا ونحن نأكل، فيقول: لا تقارونوا، فإن النبى نهى عن الإقران، ثم يقول: "إلا أن يستأذن الرجل أخاه" ((متفق عليه))
We were with 'Abdullah bin Az-Zubair (May Allah be pleased with them) in a time of famine, then we were provided with dates. (Once) when we were eating, 'Abdullah bin 'Umar (May Allah be pleased with them) passed by us and said: "Do not eat two dates together, for Messenger of Allah (ﷺ) prohibited it, unless one seeks permission from his brother (partner)." [Al-Bukhari and Muslim].
In plain words
When people share from one pile of food, no one should take two pieces at once unless his companion agrees. Simple fairness so that all eat their share, especially in times of scarcity.
Reference : Riyad as-Salihin 741 In-book reference : Book 2, Hadith 15