It is disliked to be overly meticulous with the details of engraving in the mihrab because it distracts the worshiper. This is the basis for the prohibition against excessive decoration. However, it is permissible to engrave and decorate the mosque with plaster, gold water, and other materials without excessiveness, as it serves to honor the mosque and glorify the religion. The Kaaba has been decorated with gold and silver water and covered with colored silk as a sign of reverence. However, it is preferable and better to spend the money used for decoration on the needy. See: Tabyin al-Haqa'iq 1: 168.