Does one sin if one curses others—including one's family and parents—in one's mind, even if the cursing sometimes reaches the point of disbelief?

Mere self-talk, without moving the tongue, is not held against a person, as the Prophet, peace and blessings be upon him, said: "Indeed, Allah has forgiven for my Ummah whatever whispers or thoughts cross their minds, so long as they do not act upon it or speak of it." However, one must strive to accustom the soul to speak good and truth, and to distance it from whispers and idleness, and to occupy time with beneficial deeds such as memorizing the Qur'an and studying books of Sunnah and Sirah.