What is the ruling on selling a gold piece at a public auction between the sermon and the two Khutbahs on Friday inside the mosque to complete its construction, knowing that the piece was donated?

If the sale occurs at the time of the second adhan and the Imam ascending the minbar, then it is forbidden (haram) and is invalidated (فسخ) according to the Malikis and those who agree with them, if both parties or one of them is obliged to attend Jumu'ah prayer. However, if the sale takes place after the zenith (zawal) and before the Imam appears and the adhan, it is considered disliked (makruh) by the Shafi'is. Buying and selling in the mosque is disliked at all times, and it is prohibited if it involves brokerage.