"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»