the Messenger of Allah forbade selling fruits before they ripen. It was said: "O Messenger of Allah what does ripen mean?" he said: 'when they turn red." And the Messenger of Allah said: "What do you think if Allah withholds the fruits (causes it not to ripen), why would any one of you take his brother's wealth?" (Using translation from Nasāʾī 4526)  

أَنَّ رَسُولَ اللهِ ﷺ نَهَى عَنْ بَيْعِ الثِّمَارِ حَتَّى تُزْهِيَ قِيلَ يَا رَسُولَ اللهِ وَمَا تُزْهِيَ؟ قَالَ «حَتَّى تَحْمَرَّ» وَقَالَ رَسُولُ اللهِ ﷺ «أَرَأَيْتَ إِنْ مَنَعَ اللهُ الثَّمَرَةَ فَبِمَ يَأْخُذُ أَحَدُكُمْ مَالَ أَخِيهِ؟»