"We used to buy food from troops of riders (i.e., the caravans) without knowing the amount, but the Messenger of Allah ﷺ forbade us to sell it until it had been delivered to us." (Using translation from Ibn Mājah 2229)
كُنَّا نَشْتَرِي الطَّعَامَ مِنَ الرُّكْبَانِ جُزَافًا فَنَهَانَا رَسُولُ اللهِ ﷺ أَنْ نَبِيعَهُ حَتَّى نَنْقُلَهُ مِنْ مَكَانِهِ