Question: Some people do not practice Islaam at all. They do not recite Qur’aan or even know one Aayah of it. They do not offer Salaah (prayer) nor pay Zakaah (obligatory charity). They even curse the religion and the Messenger of Allaah (peace be upon him). What is worse is that they curse Allaah, daily, yet still claim to be Muslims who testify that there is no deity except Allaah and that Muhammad is His Messenger. Is it permissible to eat the meat of their slaughtered animals, even though in our society there are so many of such people.
Answer: First of all: Abandonment of Salaah and denying its obligation is an act of Kufr (disbelief) according to Ijma‘ (consensus) of scholars. Similarly, the abandonment of Salaah due to laziness and carelessness is also an act of Kufr according to the more preponderant of the two opinions held by the scholars… read more here.