Is it permissible for the price of the sold item to be a known benefit?

There is no objection to making a known benefit the price of a sold item, such as building a house, tailoring, or providing a month's service. This is supported by the statement of Imam An-Nawawi: "It is permissible to make a benefit a price, a wage, or a dowry." And by Al-Hajjawi's definition of sale: "It is the exchange of property, even if in debt, or a permissible benefit, such as a right of way through a house, for a similar item from either on a perpetual basis."