Does agreeing on matters concerning the costs of work in the mosque fall under the prohibition of buying and selling in it?

It is not permissible to buy and sell in the mosque, and such transactions are invalid; this is based on the words of the Messenger of Allah, peace and blessings be upon him: "The Messenger of Allah, peace and blessings be upon him, forbade buying and selling in the mosque," and his saying: "If you see someone buying or selling in the mosque, say: 'May Allah not profit your trade!'"

Buying, selling, and renting are forbidden in the mosque for both the one in i'tikaf (spiritual retreat) and others, regardless of whether the item sold is small or large. If such an act is performed, it is null and void.

Renting falls under the ruling of selling. Therefore, it is not permissible to enter into contracts for work wages or the price of materials and the like inside the mosque, even if it is for the benefit of the mosque. Instead, one should do so outside of it.