Anas b. Malik (Allah be pleased with him) reported that Allah's Messenger (ﷺ) forbade the sale of fruits until these are mellow. They (the companions of Anas) said:

What is meant by" mellow"? He said: It implies that these became red. He said: When Allah hinders the growth of fruits, (then) what for the wealth of your brother would become permissible for you?

حَدَّثَنِي أَبُو الطَّاهِرِ، أَخْبَرَنَا ابْنُ وَهْبٍ، أَخْبَرَنِي مَالِكٌ، عَنْ حُمَيْدٍ الطَّوِيلِ، عَنْ أَنَسِ، بْنِ مَالِكٍ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم نَهَى عَنْ بَيْعِ الثَّمَرَةِ حَتَّى تُزْهِيَ قَالُوا وَمَا تُزْهِيَ قَالَ تَحْمَرُّ ‏.‏ فَقَالَ إِذَا مَنَعَ اللَّهُ الثَّمَرَةَ فَبِمَ تَسْتَحِلُّ مَالَ أَخِيكَ .