Abandoning ṣalāh is among the gravest of sins: the Prophet (ṣallallāhu ʿalayhi wa sallam) said, "Between a man and shirk and kufr is the abandonment of prayer," and Allah describes the people of Saqar answering, "What put you into Saqar? They will say: We were not of those who prayed" (74:42-43), and warns of "successors who neglected prayer and pursued desires, so they are going to meet evil" (19:59). Whoever denies that prayer is obligatory has left Islam by consensus. As for one who affirms its obligation but abandons it out of laziness, there is well-known ikhtilāf: Imam Aḥmad and a large group of the Salaf — and contemporary scholars such as Ibn Bāz and Ibn ʿUthaymīn — held this is major kufr taking him out of Islam, while Abū Ḥanīfah, Mālik and al-Shāfiʿī held it is a major sin short of disbelief. This is a ruling on the act in general; declaring a specific individual a disbeliever is the affair of qualified scholars and judges, not of ordinary people, and it requires establishing the proof and removing any doubt. The duty of the layman is to call such a person back to prayer with wisdom and gentleness, not to pass sentence on him.
Q&A · Prayer
What is the ruling on someone who does not pray at all?
Evidence — the daleel
On deen2u
Informational, not a personal fatwa. Consult a qualified scholar for rulings on your situation.