there is no such thing as unforgivable sins. whether its stealing candy or murdering someone, God forgives.
However, if you want a Biblical answer then blasphemy is an
UNFORGIVABLE sin.
- LUKE 12:10, "And everyone that says a word against the Son of Man, that will be forgiven; But he that blasphemes against The Holy Spirit will not be forgiven."
- MARK 3:29, "Whoever blasphemes against The Holy Spirit will never have forgiveness, but is guilty of everlasting sin."
- MATTHEW 12: 31-32 "Therefore I say to you, any sin and blasphemy shall be forgiven men, but blasphemy against the Spirit shall not be forgiven. And whoever shall speak a word against the Son of Man, it shall be forgiven him; but whoever shall speak against the Holy Spirit, it shall not be forgiven him, either in this age, or in the age to come".