From whom is a valid oath established?

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A valid oath is established only from a legally responsible person (mukallaf) who is choosing freely and intending to take an oath. It is not valid from someone who is not legally responsible, such as a child, an insane person, or one who is sleeping, based on the saying of the Prophet (peace be upon him): "The pen is lifted from three [people]." Moreover, an oath involves a duty regarding a right, thus it cannot be validly uttered by one who is not legally responsible.