Types of Unprescribed Vows

The question: The following message was received by the program from the questioner Abbas Jadah al-Janabi, from the city of al-Musayyib in the province of Babil, in the Republic of Iraq. He says in his message: Your program is one of the successful programs that serve Muslims and guide them to the right path, and you are to be thanked for this, if Allah wills.
First question: I previously made a vow for the sake of Allah the Exalted, on the condition that this vow be without negotiation, meaning: without discussing the price when buying. When I went to the market, a merchant offered me an item for eighty dinars, although I knew that the item was worth only thirty dinars. So I negotiated with the seller and bought the item for a lower price. Has the vow become permissible or not? Please inform us, may Allah reward you.

Answer: This vow is an unprescribed vow, because there is nothing wrong with negotiation; and because many people may raise the price without right, so negotiation is needed. The Prophet (peace and blessings be upon him) negotiated with Jabir over a camel, and he (peace and blessings be upon him) discussed the price with him. So the point is: your vow that you would not negotiate is an unprescribed vow. You may negotiate over goods until you buy them at the appropriate price known in the markets. You must pay the expiation for an oath for this. You must pay the expiation for an oath for this vow, which is: feeding ten poor people, or clothing them, with approximately one and a half kilograms of dates, rice, or other staple food of the country for each poor person. And you may negotiate. Yes.