"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)
قُلْتُ يَا رَسُولَ اللهِ يَأْتِينِي الرَّجُلُ يَسْأَلُنِي الْبَيْعَ لَيْسَ عِنْدِي أَبِيعُهُ مِنْهُ ثُمَّ أَتَكَلَّفُهُ لَهُ مِنَ السُّوقِ قَالَ لَا تَبِعْ مَا لَيْسَ عِنْدَكَ