The ruling on selling what one does not own at the time of the contract

The Shaykh:
If the one who sold it to him is his father, this is not permissible because he sold what he does not own. There is an error in this, and perhaps the owner of the goods will sell it, or he will not sell it except for a very high price, which harms the seller, or he sells it for a cheap price and the buyer is harmed. He says to him, "I went and bought it here for the cheapest price," so regret occurs. The Prophet (peace and blessings be upon him) said to Hakim regarding the matter of commitment as follows: . Now they do this: they go to an installment store, or a bank, or other institutions, and they agree on a specific piece of land, a specific building, or a specific car. They finalize the contract and the specifications, and both parties sign. Then the seller goes and buys it and delivers it to the buyer. This is selling what he does not have, and it is forbidden, and the contract is invalid. Yes, he tells him, "Go, when the one in need comes to the store owner who sells to people, and he says to the store owner, 'What land pleases you, or what car pleases you, or what item pleases you among the people? Just bring me its value, determine its value, and I will buy it and sell it and deliver it to you. I will buy it and deliver it to you. But come, I am afraid it will become cheap, or I am afraid I will not be able to exchange it for you. Come, let us write a document and a contract for you, and you deliver the price or part of the price to me, I am afraid it will become cheap.' So he does not go to buy the goods until he has secured it for the buyer before he owns it. This is an invalid sale, and I seek refuge in Allah, selling what one does not own. However, if the goods are present with the store owner or the institution, the cars are present, the lands are present, the buildings are present, then there is no harm in selling to whoever comes to him, for a cash price or a deferred price, because he sold something he owns at the time of the contract. It does not help to say, "This is a promise to sell," or "This is an order to sell," or similar empty talk. All of this has no value; all of it has no value. The Messenger (peace and blessings be upon him) said: at the time of the contract. If the thing you want to sell is with you at the time of the contract, meaning it is in your ownership, yes. And it is not permissible that you sell something you have not yet taken possession of or obtained. This is not permissible; this is selling what one does not own.