The Ruling on Selling What the Seller Does Not Have and Then Buying It

Question:
Honorable Shaykh, may Allah grant you success. A questioner says: A seller does not have the requested item in his possession; rather, he contracts with the customer for an item, and the customer gives him the money. Then he goes and buys this item. So he contracts with the customer, the customer gives him the money, then this seller goes and buys the item and takes a profit on it. Is this transaction permissible?

Answer:
And the Messenger (peace and blessings be upon him) said: If he has the item, he sells it. If he does not have it, no. He does not sell it and then go buy it from the market. This is not permissible. He does not sell except something he owns at the time of the contract.