The ruling on selling a commodity before taking possession of it

Question:
May Allah reward you. The brother Abu 'Abd al-Rahman sent this question, saying: Honorable Shaykh, peace be upon you, and Allah's mercy and blessings. A colleague comes to me and asks me to buy a computer for him, and we agree on the price and the details. Then I go and buy the device from one of the shops and take possession of it, and after that I sell it to my colleague according to what we agreed upon. My question, may Allah bless you, is: Is selling in this manner permissible? And if it is not permissible, what is the obligation regarding the previous sale?

Answer:
It is obligatory for one who wants to sell goods to people on credit to have them in his possession before the customers come to him. Then, when the customer comes, he sells to him from what he has. As for him agreeing with the customer when he has nothing, and then going to buy it, the Prophet (peace and blessings be upon him) forbade this, as in the hadith of Hakim ibn Hizam, where he asked the Prophet (peace and blessings be upon him) about a man who comes to him and asks to buy from him when he does not have it, so he goes and buys it from the market. He said (peace and blessings be upon him): It is obligatory for one who wants to sell goods and trade in them to have them in his shop or in his warehouse. So when the customers come, he sells to them what is suitable for them. Yes.