Sahih Muslim 1529
Sahih Muslim · Book 21: The Book of Transactions · It is invalid to sell goods before taking possession of them
Jabir b. Abdullah (Allah be pleased with them) reported Allah's Messenger (ﷺ) as saying:
حَدَّثَنَا إِسْحَاقُ بْنُ إِبْرَاهِيمَ ، أَخْبَرَنَا رَوْحٌ ، حَدَّثَنَا ابْنُ جُرَيْجٍ ، حَدَّثَنِي أَبُو الزُّبَيْرِ ، أَنَّهُ سَمِعَ جَابِرَ بْنَ عَبْدِ اللَّهِ ، يَقُولُ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يَقُولُ " إِذَا ابْتَعْتَ طَعَامًا فَلاَ تَبِعْهُ حَتَّى تَسْتَوْفِيَهُ " .
When you purchase foodgrains, do not sell them until you have taken possession of them.