What is the ruling on one who harms, prevents, or kills a person who invokes blessings upon the Prophet Muhammad (peace be upon him), and is bothered by such invocation?

Praying upon the Prophet, peace and blessings be upon him, is a great act of worship. It is not permissible to prevent someone from performing this devotion or to harm them because of it; rather, they must be respected. If their action is an innovation, then they should be advised and the truth explained to them. The basic principle regarding raising one's voice with remembrance (dhikr), recitation (tilawah), or prayers upon the Prophet, peace and blessings be upon him, is permissibility, as long as it does not disturb those praying or annoy those sleeping.