What is the maximum extent of a bequest (Wasiyyah) if the deceased leaves behind a fixed-share inheritor (Dhu Fard)?

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If the deceased leaves behind an inheritor with a fixed share (Dhu Fard), such as a daughter or a mother, the bequest cannot exceed one-third (Thuluth) of the estate. This ruling is based on the incident where Sa'd asked the Prophet, peace be upon him, if he could bequeath his entire estate save for his daughter, and the Prophet prevented him from exceeding one-third. Furthermore, since the fixed-share heir is entitled to the entire estate via their fixed share and the return (Radd), the bequest is likened to the case of residuary heirs (Asabah). This restriction applies even if the fixed-share heir has a spouse or if the deceased has a wife, because the bequest diminishes their due right, as the fixed share is earned only after accounting for bequests and debts, according to the Quranic statement: {after any bequest he may bequeath or debt} (Quran 4:11).