Narrated Tawus:Ibn `Abbas said, "Allah's Messenger (ﷺ) forbade the selling of foodstuff before its measuring and transferring into one's possession." I asked Ibn `Abbas, "How is that?" Ibn `Abbas replied, "It will be just like selling money for money, as the foodstuff has not been handed over to the first purchaser who is the present seller."
حَدَّثَنَا مُوسَى بْنُ إِسْمَاعِيلَ، حَدَّثَنَا وُهَيْبٌ، عَنِ ابْنِ طَاوُسٍ، عَنْ أَبِيهِ، عَنِ ابْنِ عَبَّاسٍ ـ رضى الله عنهما ـ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم نَهَى أَنْ يَبِيعَ الرَّجُلُ طَعَامًا حَتَّى يَسْتَوْفِيَهُ. قُلْتُ لاِبْنِ عَبَّاسٍ كَيْفَ ذَاكَ قَالَ ذَاكَ دَرَاهِمُ بِدَرَاهِمَ وَالطَّعَامُ مُرْجَأٌ. قَالَ أَبُو عَبْد اللَّهِ مُرْجَئُونَ مُؤَخَّرُونَ
Bukhari
Sales and Trade • Hadith 84