The Ruling of the One who Stops Performing Prayer

1- The one who stops performing As-Salah due to denying its obligation:

If he is ignorant about the issue, then he should be informed. Subsequently if he persists on rejecting its obligation, he becomes a disbeliever, as he belies Allah Almighty, His Messenger ﷺ and the consensus of the Muslims.2- The one who stops performing prayer out of laziness:

Whosoever stops performing As-Salah intentionally out of laziness, has disbelieved. It is upon the ruler to order him to perform As-Salah and also advise him, for three days, to repent for abandoning it. Subsequently, if he repents and returns to making the As-Salah, he is spared. But if he does not start praying again, he is killed for apostasy. This is in accordance with the Prophet’s ﷺ statement:
“The covenant which is between us and them (the disbelievers) is the prayer; so whosoever leaves it has disbelieved.”
[ Source: At-Tirmidhi.] Also his saying:
“Indeed between a man, and shirk and kufr, is abandoning As-Salah.”
[ Source: Muslim.]
source: islamkingdom