Abu Bakhtari reported:

I asked Ibn 'Abbas (Allah be pleased with them) about the sale of dates. He said: Allah's Messenger (ﷺ) forbade the sale of dates of the trees until one eats them or they are eaten (i. e. they are fit to be eaten) or until they are weighed (or measured). I said: What does it imply:" Until it is weighed"? Thereupon a person who was with him (Ibn Abbas) said: Until he is able to keep it with him (after plucking them).

حَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، وَابْنُ، بَشَّارٍ قَالاَ حَدَّثَنَا مُحَمَّدُ بْنُ جَعْفَرٍ، حَدَّثَنَا شُعْبَةُ، عَنْ عَمْرِو بْنِ مُرَّةَ، عَنْ أَبِي الْبَخْتَرِيِّ، قَالَ سَأَلْتُ ابْنَ عَبَّاسٍ عَنْ بَيْعِ النَّخْلِ، فَقَالَ نَهَى رَسُولُ اللَّهِ صلى الله عليه وسلم عَنْ بَيْعِ النَّخْلِ حَتَّى يَأْكُلَ مِنْهُ أَوْ يُؤْكَلَ وَحَتَّى يُوزَنَ ‏.‏ قَالَ فَقُلْتُ مَا يُوزَنُ فَقَالَ رَجُلٌ عِنْدَهُ حَتَّى يَحْزَرَ ‏.‏