Someone asking another to buy him a commodity for cash and then reselling it to him with deferred payment

Q: A man asks his friend to buy a car for him in cash, then he sells it to him for a deferred payment with extra money as a profit. In other words, when he buys the car for 1,000 Riyals in cash, he sells it back to his friend for say 1,100 Riyals for a specified term. Is this regarded as Riba (usury/interest)? Would you please clarify the statement of Imam Malik (may Allah be merciful to him) that he was informed that the Messenger of Allah (peace be upon him) forbade two sales in one? In addition, please tell us about some other kinds that fall into the category of forbidden sales. (Part No. 13; Page No. 153

A: If a person asks someone to buy a specific car for him or a car that meets certain requirements that he stipulates, and promises to buy it from him, and he buys it from the one whom he asked to do that and takes possession of it, it is permissible for the one who asks for it to buy it from him after it is paid in cash or by installments with a specific amount of extra money as profit. This is not a form of selling what one does not have, because the one who is asking for this product is selling it to the one who asked for it. This is done after buying it and taking possession of it. He does not have the right to sell it to his friend, for example, before he buys it, or after he buys it and before he takes possession of it, because the Prophet (peace be upon him) forbade selling goods until the merchant takes possession of them.With regard to the Hadith of the Prophet in which he forbade two sales in one, the Jumhur (dominant majority of scholars) are of the opinion that it means that the seller says to the buyer, "I sell you this commodity for 10 Dirhams in cash or for 15 Dirhams which should be paid within, say a year". Another case is where the seller may say, "I sell you one of the two cows for say, 1,000 Riyals." Once the buyer shows his acceptance, they part without agreeing on the method of payment whether it is cash or deferred as is in the first case, and without agreeing on which cow should be sold as is in the second case. This kind of transaction is forbidden because the method of payment was not decided and accordingly, as in the first case, an agreement was not made about the commodity as in the second case.Moreover, the Jumhur said that this ruling applies to the person who says to someone else, "I sell you (Part No. 13; Page No. 154) my house for such and such, providing that you sell me your house for such and such, or you work for me for a month and be paid such and such, or I marry your daughter for such and such, or you marry my daughter for such and such. All these kinds of transactions are not valid as they imply conducting two transactions in one which was forbidden by the Prophet (peace be upon him). `Inah sale (selling and delivering something to another person in installments but repurchasing it with less immediate cash) is also regarded as an example of conducting two transactions in one.It will be better for you to read the book entitled Al-Mughny written by Ibn Qudamah (may Allah be merciful to him) concerning this issue and the commentary written by Ibn Al-Qayyim on the Hadith of the Prophet (peace be upon him) in which he forbade conducting two sales in one in the books Tahdhib Al-Sunan and I`lam Al-Mowqi`in. May Allah grant us success. May peace and blessings of Allah be upon our Prophet Muhammad, his family and Companions!