Narrated Abu Al-Bakhtari:

I asked Ibn Umar about Salam (the fruits of) date-palms. He replied, "The Prophet forbade the sale of dates till their benefit becomes evident and fit for eating and also the sale of silver (for gold) on credit." I asked Ibn 'Abbas about Salam for dates and he replied, "The Prophet forbade the sale of dates till they were fit for eating and could be estimated."

حَدَّثَنَا أَبُو الْوَلِيدِ، حَدَّثَنَا شُعْبَةُ، عَنْ عَمْرٍو، عَنْ أَبِي الْبَخْتَرِيِّ، قَالَ سَأَلْتُ ابْنَ عُمَرَ ـ رضى الله عنهما ـ عَنِ السَّلَمِ، فِي النَّخْلِ فَقَالَ نُهِيَ عَنْ بَيْعِ النَّخْلِ، حَتَّى يَصْلُحَ، وَعَنْ بَيْعِ الْوَرِقِ، نَسَاءً بِنَاجِزٍ. وَسَأَلْتُ ابْنَ عَبَّاسٍ عَنِ السَّلَمِ، فِي النَّخْلِ، فَقَالَ نَهَى النَّبِيُّ ﷺ عَنْ بَيْعِ النَّخْلِ حَتَّى يُؤْكَلَ مِنْهُ، أَوْ يَأْكُلَ مِنْهُ، وَحَتَّى يُوزَنَ.