Sahih Bukhari Volume 3, Book 34, Hadith 2173

حَدَّثَنَا أَبُو النُّعْمَانِ، حَدَّثَنَا حَمَّادُ بْنُ زَيْدٍ، عَنْ أَيُّوبَ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ ـ رضى الله عنهما ـ أَنَّ النَّبِيَّ صلى الله عليه وسلم نَهَى عَنِ الْمُزَابَنَةِ قَالَ وَالْمُزَابَنَةُ أَنْ يَبِيعَ الثَّمَرَ بِكَيْلٍ، إِنْ زَادَ فَلِي وَإِنْ نَقَصَ فَعَلَىَّ‏.‏

Narrated By Ibn 'Umar : The Prophet forbade Muzabana; and Muzabana is the selling of fresh fruit (without measuring it) for something by measure on the basis that if that thing turns to be more than the fruit, the increase would be for the seller of the fruit, and if it turns to be less, that would be of his lot.