The Right to be Imaam

Q: Salaah-384: Although we have an appointed Imaam in our Masjid, we sometimes have an Aalim or Qaari better than him who visits. Who is then more worthy of being the Imaam?

Answer: Even if the other person has more knowledge and reads better, the appointed Imaam still has a greater right to lead the salaah. It is therefore wrong to force the Imaam to allow the newcomer to lead the salaah and such a newcomer should also not be as bold as to step forward unless the Imaam permits him. And Allaah knows best what is most correct.

Fatawa Rahimiyyah vol.2