وَعَنِ اِبْنِ عَبَّاسٍ رَضِيَ اَللَّهُ عَنْهُمَا
قَالَ: «نَهَى رَسُولُ اَللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: أَنْ تُبَاعَ ثَمَرَةٌ حَتَّى تُطْعَمَ، وَلَا يُبَاعَ صُوفٌ عَلَى ظَهْرٍ، وَلَا لَبَنٌ فِي ضَرْعٍ»
The Messenger of Allah (sallallahu alayhi wa sallam) forbade the selling of a fruit till it becomes ripe, or the selling of fur which is (still) on the back (of an animal) or milk which is (still) in the udder.
Bulugh al-Maram 942, Book 7, Business Transactions, Hadith 53. 1 min read