Wa `alaykum As-Salamu waRahmatullahi wa Barakatuh.

 

No, it is not permissible to do so because it may lead committing shirk or praying towards the tomb. A dead person should be buried at the grave yard. The Prophet warned us again this practice by saying, “Let there be curse of Allah upon the Jews and the Christians for they have taken the graves of their apostles as places of worship.“ (Muslim)

 

Prophets are exempted from this because they are supposed to be buried at where they die. The Prophet’s grave was outside his mosque. It became a part of the masjid later when Muslims felt it necessary to expand the building of the mosque.

 

Almighty Allah knows best.