"I said: 'O Messenger of Allah, a man is asking me to sell him something that I do not possess; Shall I sell it to him?' He said: 'Do not sell what is not with you."'  

قُلْتُ يَا رَسُولَ اللَّهِ الرَّجُلُ يَسْأَلُنِي الْبَيْعَ وَلَيْسَ عِنْدِي أَفَأَبِيعُهُ قَالَ لاَ تَبِعْ مَا لَيْسَ عِنْدَكَ  

"The Messenger of Allah ﷺ said: 'It is not permissible to sell something that is not with you, nor to profit from what you do not possess."'  

قَالَ رَسُولُ اللَّهِ ﷺ لاَ يَحِلُّ بَيْعُ مَا لَيْسَ عِنْدَكَ وَلاَ رِبْحُ مَا لَمْ يُضْمَنْ  

when the Messenger of Allah ﷺ sent him to Makkah, he forbade him from profiting off of what he did not possess.  

لَمَّا بَعَثَهُ رَسُولُ اللَّهِ ﷺ إِلَى مَكَّةَ نَهَاهُ عَنْ شِفِّ مَا لَمْ يُضْمَنْ