Is the wife forbidden if the husband said to himself – without uttering the words – "If I don't win, then my wife is forbidden to me until the Day of Judgment," and he did not win, and the intention was only for motivation?

If the matter did not exceed a mere thought (حديث النفس) of prohibiting the wife, then nothing is incumbent upon him, due to the saying of the Prophet, peace and blessings be upon him: "Indeed, Allah has overlooked for my Ummah what they merely think to themselves, as long as they do not speak of it or act upon it."