that the Messenger of Allah said: "It is not permissible to lend on the condition of a sale, or to have two conditions in one transaction, or to sell what you do not have." (Sahih (Using translation from Nasāʾī 4611)  

أَنَّ رَسُولَ اللهِ ﷺ قَالَ «لَا يَحِلُّ سَلَفٌ وَبَيْعٌ وَلَا شَرْطَانِ فِي بَيْعٍ وَلَا بَيْعُ مَا لَيْسَ عِنْدَكَ»  

"The Messenger of Allah said: 'No man is bound by a transaction involving the sale of something that he does not possess.''' (Using translation from Nasāʾī 4612)  

قَالَ رَسُولُ اللهِ ﷺ «لَيْسَ عَلَى الرَّجُلِ بَيْعٌ فِيمَا لَا يَمْلِكُ»  

"I asked the Prophet "O Messenger of Allah, a man may come to me and ask me to sell him something that I do not have. Can I sell it to him then go and buy it from the market?' He said: 'Do not sell what you do not have.''' (Using translation from Nasāʾī 4613)  

سَأَلْتُ النَّبِيَّ ﷺ قُلْتُ يَا رَسُولَ اللهِ يَأْتِينِي الرَّجُلُ يَسْأَلُنِي البَيْعَ لَيْسَ عِنْدِي أَبِيعُهُ مِنْهُ ثُمَّ أَبْتَاعُهُ لَهُ مِنَ السُّوقِ؟ فَقَالَ «لَا تَبِعْ مَا لَيْسَ عِنْدَكَ»  

[Machine] I said, "O Messenger of Allah, I buy goods, so what is permissible for me and what is prohibited for me?" He said to me, "When you sell something, do not sell it until you possess it."  

قُلْتُ يَا رَسُولِ اللهِ إِنِّي أَشْتَرِي بُيُوعًا فَمَا يَحِلُّ لِي وَمَا يَحْرُمُ عَلَيَّ؟ فَقَالَ لِي «إِذَا بِعْتَ شَيْئًا فَلَا تَبِعْهُ حَتَّى تَقْبِضَهُ»