the Prophet forbade selling fresh dates still on the tree for dried dates. Ibn 'Umar said: "Azid bin Thabit narrated to me, that Messenger of Allah permitted that in the case o 'Ayaya"'  

أَنَّ النَّبِيَّ ﷺ نَهَى عَنْ بَيْعِ الثَّمَرِ بِالتَّمْرِ وَقَالَ ابْنُ عُمَرَ حَدَّثَنِي زَيْدُ بْنُ ثَابِتٍ أَنَّ رَسُولَ اللَّهِ ﷺ رَخَّصَ فِي الْعَرَايَا  

the Messenger of Allah forbade Muzabanah. Ad Muzabanah is when what is art the tops of the trees is sold for a certain amount f dried dates; if there are more then I gain, and if there are less the I lose.  

أَنَّ رَسُولَ اللَّهِ ﷺ نَهَى عَنِ الْمُزَابَنَةِ وَالْمُزَابَنَةُ أَنْ يُبَاعَ مَا فِي رُءُوسِ النَّخْلِ بِتَمْرٍ بِكَيْلٍ مُسَمًّى إِنْ زَادَ لِي وَإِنْ نَقَصَ فَعَلَىَّ