What is the ruling on praying in a mosque that contains a shrine? And what is the reason for burying the dead—especially the righteous—in mosques, and in which era did this begin, and is this practice limited to Egypt or does it include other countries?

The phenomenon of building mosques over graves, or burying the dead within mosques, is widespread in Egypt and some Islamic countries. This practice was not known during the early Islamic period; rather, it emerged after the appearance of esoteric (Batinī) sects that introduced innovations (bid'ah) and superstitions.