He endowed a piece of land to build a mosque, then changed his mind

There is a rich person among us who donated some land to build a mosque, then someone came along and asked him to make it a school. What should he do?

Praise be to Allah, and blessings and peace be upon the Messenger of Allah:

If the man has already donated the piece of land for building a mosque, then it should be used for that purpose, and he cannot go back on his donation. But if it is the case that all that has happened is a promise to donate land for a mosque, it is better for him to keep his promise. May Allaah bless our Prophet Muhammad and his family and companions.