The Book of Transactions
حَدَّثَنِي عَلِيُّ بْنُ حُجْرٍ السَّعْدِيُّ، وَزُهَيْرُ بْنُ حَرْبٍ، قَالاَ حَدَّثَنَا إِسْمَاعِيلُ، - وَهُوَ ابْنُ إِبْرَاهِيمَ - عَنْ أَيُّوبَ، 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 فَلِي وَإِنْ نَقَصَ فَعَلَىَّ .Ibn 'Umar (Allah be pleased with them) reported Allah's Messenger (ﷺ) having forbidden Muzabana, and Muzabana implies the selling of dry dates for fresh dates on the tree with a definite measure (making it clear) that in case it increases, it belongs to me and if it is less, it is my responsibility
From Sahih Muslim, whose reports the scholars accept as authentic.