What is this belief called?

Question

There is a belief that according to Hebrews 10:26, the "unforgivable sin" is sinning willfully after having been saved. What is this belief called and what is its theological origin? I'm not asking for it to be refuted, I just want to know the name

Answer 1

Assuredly, I say to you, all sins will be forgiven the sons of men, and whatever blasphemies they may utter; but he who blasphemes against the Holy Spirit never has forgiveness, but is subject to eternal condemnation
— Mark 3:28–29

And anyone who speaks a word against the Son of Man, it will be forgiven him; but to him who blasphemes against the Holy Spirit, it will not be forgiven.
— Luke 12:10

Some translations (e.g. Mark 3 (NKJV)) add a title to this: "The Unpardonable Sin".

Not all denominations believe that it refers to "sinning willfully after having been saved" though.

Rather it refers to a deliberate rejection of, or refusal to accept, God's holy spirit and the salvation it offers. When one has the spirit, God will forgive anything one repents of. But if one does not have the spirit, one cannot be forgiven, at least not in the sense of repentance and salvation.

Eternal sin - Wikipedia gives the perspective of several denominations on the matter, but there doesn't seem to be any specific name associated with the belief.

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Note:

it would help if, instead of "There is a belief that …", the Question gave an explicit quotation and reference for this belief.

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Note #2:

apparently the "unforgivable sin" wasn't meant to refer to the "unpardonable sin". Rather, it refers to something different, Hebrews 10: 26-27, making my answer somewhat irrelevant.