Does the questioner's share of land become "cursed" and impermissible to benefit from if he had verbally declared his unwillingness to have it, by analogy with the ruling on the animal cursed by its owner? And does doubt about his saying that affect the legal ruling? And what is the ruling on applying the principle of "doubt does not negate certainty" in this case?

The hadith to which the questioner refers is what Muslim narrated from 'Imran ibn Husayn and Abu Barzah, and Ahmad narrated from 'Aishah, that the Prophet, peace and blessings be upon him, heard a woman cursing her she-camel and said: "Take what is on it and leave it, for it is accursed."

This does not mean that benefiting from an accursed thing is impermissible. The Prophet, peace and blessings be upon him, did that as a punishment for the woman.

Al-Nawawi said: There is no problem with the hadith. The intent is to forbid that she-camel from accompanying them, and it does not contain a prohibition against selling it, slaughtering it, or riding it when not accompanying the Prophet, peace and blessings be upon him.

Based on this, it is not forbidden to benefit from an accursed thing or to give it as charity. Your ownership of your share of it has not ceased, and you can sell it or keep it.

The rule "Certainty is not removed by doubt" is correct, and the one who acts upon it is excused.