1. Associating partners with Allah (Shirk) (1 of 7 fatal Sins)
Surely, Allah does not forgive associating anything with Him, and He forgives whatever is other than that to whomever He wills. ( 4:48 and 116)
Open Great Shirk– Idolatry: worshipping beings other than Allah
Hidden Small Shirk is called Riya – showing off or Ostentation
“Should I not inform you of that which I fear for you even more than the dangers of dajjaal?-Anti-Christ It is the hidden shirk: Riya-showing off : A person stands to pray and he beautifies his prayer because he sees the people looking at him”.
2. Committing murder : (25 68) (2 of 7 fatal Sins)
And they who do not call upon another god with Allah and do not slay the soul, which Allah has forbidden except in the requirements of justice, and (who) do not commit fornication and he who does this shall find a requital of sin (25 68)
3. Practising black magic (2: 102) This even takes one out of the folds of Islam
Three do not enter heaven : the alcoholic, the severer of the bonds of kinship, and the one who believes in magic.