Is it considered disbelief to imagine saying or actually saying, "That person is a disbeliever," with the intention that their action is not from the religion?

A mere contradiction between an action and religion or certain religious texts does not necessitate excommunication (takfir). Rather, the act or statement must be actual disbelief (kufr) according to the scale of Sharia. Takfir is a legal ruling that cannot be approached based on personal opinion. A Muslim should not be excommunicated unless the Qur'an and Sunnah indicate their disbelief, and the conditions for takfir are met, and its impediments are absent. Whoever declares a Muslim an unbeliever, when they are not, has incurred a great sin, for the Prophet, peace and blessings be upon him, said: "Any man who says to his brother, 'O disbeliever,' then it has returned upon one of them." This means the deficiency returns to him or it is a declaration of excommunication, not actual disbelief, or it is interpreted as applicable to one who deems the forbidden permissible. As for merely thinking that someone is an unbeliever, this does not fall under the ruling of one who declares disbelief with their tongue, because Allah has forgiven this Ummah for what they ponder within themselves, as long as they do not act upon it or speak of it. One must also be wary of having ill thoughts about Muslims.