Sahih Bukhari Volume 3, Book 35, Hadith 2248

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 صلى الله عليه وسلم عَنْ بَيْعِ النَّخْلِ حَتَّى يُؤْكَلَ مِنْهُ، أَوْ يَأْكُلَ مِنْهُ، وَحَتَّى يُوزَنَ‏

Narrated By 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."