Sahih al-Bukhari 2249, 2250
Narrated Abu Al-Bakhtari:
I asked Ibn `Umar about Salam for dates. Ibn `Umar replied, "The Prophet (ﷺ) forbade the sale (the fruits) 
of date-palms until they were fit for eating and also forbade the sale of silver for gold on credit." I also 
asked Ibn `Abbas about it. Ibn `Abbas replied, "The Prophet (ﷺ) forbade the sale of dates till they were fit 
for eating, and could be weighed." I asked him, "What is to be weighed (as the dates are on the 
trees)?" A man sitting by Ibn `Abbas said, "It means till they are cut and stored."
حَدَّثَنَا مُحَمَّدُ بْنُ بَشَّارٍ، حَدَّثَنَا غُنْدَرٌ، حَدَّثَنَا شُعْبَةُ، عَنْ عَمْرٍو، عَنْ أَبِي الْبَخْتَرِيِّ، سَأَلْتُ ابْنَ عُمَرَ ـ رضى الله عنهما ـ عَنِ السَّلَمِ، فِي النَّخْلِ فَقَالَ نَهَى النَّبِيُّ صلى الله عليه وسلم عَنْ بَيْعِ الثَّمَرِ حَتَّى يَصْلُحَ، وَنَهَى عَنِ الْوَرِقِ بِالذَّهَبِ نَسَاءً بِنَاجِزٍ‏.‏ وَسَأَلْتُ ابْنَ عَبَّاسٍ فَقَالَ نَهَى النَّبِيُّ صلى الله عليه وسلم عَنْ بَيْعِ النَّخْلِ حَتَّى يَأْكُلَ أَوْ يُؤْكَلَ، وَحَتَّى يُوزَنَ‏.‏ قُلْتُ وَمَا يُوزَنُ قَالَ رَجُلٌ عِنْدَهُ حَتَّى يُحْرَزَ‏.‏