The Prophet ﷺ forbade the sale of fruits till their benefit is evident; and the sale of date palms till the dates are almost ripe. He was asked what 'are almost ripe' meant. He replied, "Got red and yellow."  

عَنِ النَّبِيِّ ﷺ أَنَّهُ نَهَى عَنْ بَيْعِ الثَّمَرَةِ حَتَّى يَبْدُوَ صَلاَحُهَا وَعَنِ النَّخْلِ حَتَّى يَزْهُوَ قِيلَ وَمَا يَزْهُو قَالَ يَحْمَارُّ أَوْ يَصْفَارُّ