Is there sin incurred by the seller and the buyer if a car sale is concluded with a Muslim, after the seller had refused to sell it to a non-Muslim buyer who wished to purchase it?

It is established that there is a prohibition against a Muslim outbidding another Muslim, and the majority of scholars have extended this to include non-belligerent disbelievers. In Fath al-Bari by Ibn Hajar, regarding the hadith of Uqbah ibn Amir, it states: "A believer is the brother of another believer. It is not permissible for a believer to outbid his brother in a sale, nor to propose marriage to a woman who has already received a proposal from his brother, until the latter abandons it." The majority of scholars hold that a Dhimmi (a non-Muslim living under Muslim rule) is included with a Muslim in this ruling, and that the expression "his brother" was used to denote the common case and therefore has no restrictive meaning. Thus, if the person who came to buy the car had not yet reached the stage of agreement and commitment with the seller, there is no harm in purchasing it, and the contract is valid.