Messenger of Allah ﷺ forbade the sale of fruits till they are almost ripe. He was asked what is meant by 'are almost ripe.' He replied, "Till they become red." Messenger of Allah ﷺ further said, "If Allah spoiled the fruits, what right would one have to take the money of one's brother (i.e. other people)?"  

أَنَّ رَسُولَ اللَّهِ ﷺ نَهَى عَنْ بَيْعِ الثِّمَارِ حَتَّى تُزْهِيَ فَقِيلَ لَهُ وَمَا تُزْهِي قَالَ حَتَّى تَحْمَرَّ فَقَالَ أَرَأَيْتَ إِذَا مَنَعَ اللَّهُ الثَّمَرَةَ بِمَ يَأْخُذُ أَحَدُكُمْ مَالَ أَخِيهِ  

If somebody bought fruits before their benefit is evident and then the fruits were spoiled with blights, the loss would be suffered by the owner (not the buyer). Narrated Salim bin 'Abdullah from Ibn Umar: Messenger of Allah ﷺ said, "Do not sell or buy fruits before their benefit was evident and do not sell fresh fruits (dates) for dried dates."  

لَوْ أَنَّ رَجُلاً ابْتَاعَ ثَمَرًا قَبْلَ أَنْ يَبْدُوَ صَلاَحُهُ ثُمَّ أَصَابَتْهُ عَاهَةٌ كَانَ مَا أَصَابَهُ عَلَى رَبِّهِ أَخْبَرَنِي سَالِمُ بْنُ عَبْدِ اللَّهِ عَنِ ابْنِ عُمَرَ ؓ أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ لاَ تَتَبَايَعُوا الثَّمَرَ حَتَّى يَبْدُوَ صَلاَحُهَا وَلاَ تَبِيعُوا الثَّمَرَ بِالتَّمْرِ