Buraidah (May Allah be pleased with him) reported: Messenger of Allah (PBUH) said, “That which differentiates us from the disbelievers and hypocrites is our performance of Salat. He who abandons it, becomes a disbeliever.”
[At-Tirmidhi].
*NB: there is a difference of opinion on this matter, and the other opinion is that the muslim who doesn’t pray is still muslim, but a sinning muslim (but don’t be relieved bc leaving salaah is a grave sin)