Is it permissible to pray in a mosque that has been expanded by building and tiling over four graves, knowing that there is a prophetic hadith prohibiting that, and how can this issue be resolved without violating Islamic law?

It is not permissible to pray in mosques built over graves, because the Prophet, peace and blessings be upon him, said: "The curse of Allah is upon the Jews and Christians for taking the graves of their prophets as places of worship." The graves must be removed from the mosque. However, if removal is not possible, and the graves are ancient and not prominent, then there is no harm in praying in such a mosque. An ancient grave does not lead to fitna (temptation/strife), and the concern is with prominent graves that are worshipped besides Allah.