Q: What is the ruling on decorating the masjid with gold and silver?
A: It is impermissible to decorate the masjid or mihrab or to plate the roof or wall with gold or silver. It must be removed like all other abominations. Zakat must be paid on that amount if the niṣāb is reached.
Its removal is not required if the process renders an insignificant amount of gold or silver i.e. not enough to be of any real value.
It is also impermissible and invalid to endow gold or silver light fixtures to the masjid. Such fixtures must be removed, treated as charity, and liquidated to benefit the masjid. This ruling is like the possession of gold and silver vessels which is impermissible.
Such décor is wasteful, leads to arrogance, and is disheartening to those in need.
Source: Sharh al-Muntaha & Kashshaf al-Qina'