Is thinking about moving the tongue without uttering a sound considered an inner monologue, and is it a sin to be confused in thought about the eternity of disbelievers in Hellfire?

Avoid getting carried away with whispers (waswas) because they lead to great evil. Know that Allah has overlooked for this Ummah what their souls have dwelled upon, as long as they have not acted upon it or spoken it. Merely moving the tongue is not considered speech unless the letters emerge from their proper articulation points. Even if the person afflicted with whispers speaks that for which they would be held accountable, their speech is not blameworthy because they are in the position of one who is compelled, and one who is compelled is not held accountable, in accordance with the Prophet's (peace be upon him) saying: "Indeed, Allah has pardoned for my Ummah their mistakes, their forgetfulness, and what they are compelled to do." Ignore these whispers and strive to get rid of them.