Is the manumission (freeing of a slave) valid if performed by someone who is under legal restriction (mahjur 'alayh)?

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Manumission performed by an individual under legal restriction is invalid. This is the position held by Al-Qasim ibn Muhammad and Al-Shafi'i. The ruling is based on the principle that this act is a disposition of his property, and thus invalid, similar to all his other dispositions. Furthermore, manumission is a voluntary gift (tabarru'), resembling a gift or endowment. The restriction imposed upon him is for the preservation of his wealth for himself, therefore his manumission is not valid, just as it is invalid for a minor or an insane person.