the Messenger of Allah prohibited lending on the condition of a sale, or to have two conditions in one transaction, or to profit from what you do not posses.  

أَنَّ رَسُولَ اللَّهِ ﷺ نَهَى عَنْ سَلَفٍ وَبَيْعٍ وَشَرْطَيْنِ فِي بَيْعٍ وَرِبْحِ مَا لَمْ يُضْمَنْ