What is the ruling on purchasing a commodity with money vowed for charity to a mosque, and would the profit generated from its sale belong to the one who gave the charity or to the mosque?

Charity (sadaqah) is not binding until it is seized. So, if one intends to donate money but the money remains in their possession, they are permitted to retract and benefit from their money, and any profit in this case belongs to them. However, if the money leaves their possession and the deserving recipient seizes it, and then they reclaim it, they have clearly made a significant mistake, as it is a forbidden retraction of charity. If there is profit from this reclaimed money, jurists have differed regarding its fate. Sheikh Al-Islam Ibn Taymiyyah chose that the profit should be shared between them. As for vows (nadhr), they are not binding merely by intention; rather, speech is necessary. If you vowed to donate a specific amount for building a mosque, it is a vow of obedience that must be fulfilled, and you are only obliged to pay the vowed amount; anything in excess is a voluntary act.