What is the ruling on one who commits an act of disbelief, believing it not to be disbelief, relying on a previous fatwa?

Whoever commits an act that necessitates disbelief, while being ignorant of its implications, is not deemed a disbeliever until proof is established against them. Therefore, whoever's faith is firmly established with certainty, it does not dissipate due to doubt, except after the establishment of proof and the removal of ambiguity.