Is my request to buy the car from my friend unlawful (haram), or is it permissible (halal) for him to sell it to me after he promised another person that he would buy it from him?

If a friend promises a man to sell his car, it is commendable for him to fulfill the promise, but he is not obligated to do so according to the majority of scholars. However, the Malikis hold that he is bound by the promise if it was made for a reason or if the promisee incurred an expense based on it. If, however, the sale has already been concluded between them with offer and acceptance, but the procedures have been postponed, then the friend must complete the sale to that man, and it is forbidden for him to sell the car to you, because the Prophet, peace and blessings be upon him, said: "None of you should sell over the sale of his brother until he buys or gives up."