What is the ruling on an unconditional bequest regarding a portion of one's wealth?

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If a person declares, 'I bequeathed one-third of my wealth' (Wassaitu bi-thuluth mali), the bequest is valid. When the designated beneficiary of the bequest ceases to exist (after the extinction of the recipient), the assets are then directed towards the established purposes of an interrupted dedication (Waqf munqati').