عَنْ طَاوُوسٍ عَنِ ابْنِ عَبَّاسٍ رَضِيَ اللَّهُ عَنْهُمَا أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ نَهَى أَنْ يَبِيعَ الرَّجُلُ طَعَامًا حَتَّى يَسْتَوْفِيَهُ قَالَ فَقُلْتُ لَهُ كَيْفَ ذَلِكَ قَالَ ذَلِكَ دَرَاهِمُ بِدَرَاهِمَ وَالطَّعَامُ مُرْجَأٌ
It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) forbade a man from buying grain and then starting to sell it before taking full possession of it. Tawus says: I asked, how does this happen? He said: This becomes a sale of dirham for dirham, and the grain is left behind.