Zakat is one of the five pillars of Islam, and deliberately withholding it out of stinginess is a major sin carrying a severe warning: Allah says of those who hoard gold and silver and do not spend in His cause that these will be heated in the Fire of Hell and their foreheads, sides, and backs branded with them (Quran 9:34-35). The Prophet ﷺ also warned that the wealth of one who does not pay its zakat will be forged into plates of fire to sear him on the Day of Resurrection. Whoever denies that zakat is obligatory has left Islam, but one who withholds it while still affirming the obligation is a sinner — the ruler takes it from him by force, as Abū Bakr and the Companions did against those who refused it — yet mainstream Sunni scholars do not pronounce takfīr on such an individual.
Q&A · Zakat
What is the ruling on someone who refuses to pay zakat?
Informational, not a personal fatwa. Consult a qualified scholar for rulings on your situation.