Will a Muslim be rewarded if he abstains from something for the sake of Allah Almighty due to his belief that it is forbidden, then it becomes clear to him that it is permissible?

Intention and purpose are considered in Islamic law. Therefore, whoever abstains from something, believing it to be unlawful, and then it turns out to be lawful, is rewarded for their intention. Conversely, whoever performs an action, believing it to be unlawful, and then it turns out to be lawful, incurs sin due to their intention. Intention is the spirit of an action; an action is valid if the intention is sound and corrupt if the intention is corrupt. This is why, "Actions are but by intentions, and every person shall have but what they intended." So, whoever commits a permissible act believing it to be unlawful, such as a man who has intercourse with his wife believing her to be a stranger, is judged to be a transgressor due to his audacity towards God, even though he will not be punished with the punishment of one who commits a major sin. The opposite is also true: whoever has intercourse with a strange woman believing her to be his wife, the penalties for zina (unlawful sexual intercourse) do not apply to him, in consideration of his intention.