أَخْبَرَنِي زِيَادُ بْنُ أَيُّوبَ، قَالَ حَدَّثَنَا ابْنُ عُلَيَّةَ، قَالَ حَدَّثَنَا أَيُّوبُ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم نَهَى عَنِ الْمُزَابَنَةِ وَالْمُزَابَنَةُ أَنْ يُبَاعَ مَا فِي رُءُوسِ النَّخْلِ بِتَمْرٍ بِكَيْلٍ مُسَمًّى إِنْ زَادَ لِي وَإِنْ نَقَصَ فَعَلَىَّ ‏.‏

It was narrated from Ibn 'Umar that: 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. Translation Not Available

Book Ref: Sunan An Nisai Book 44 Hadith 4533
Web Ref:  Sunan An Nisai Vol 5 Book 44 Hadith 4537