What is the ruling regarding a bequest made contingent upon the existence of an heir who is not present?

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If a person bequeaths an amount equal to the share of an heir, assuming that heir exists, the beneficiary receives that determined amount whether the heir is actually present or not. For example, if a deceased leaves two sons and bequeaths an amount equal to the share of a third son, the legatee receives one-fourth (1/4) of the estate. Similarly, if the bequest is equal to the share of a fifth hypothetical heir, the legatee receives one-sixth (1/6). This principle applies universally. If a woman dies leaving a husband and a sister, and bequeaths an amount equal to the share of a mother if one existed, the legatee receives one-fifth (1/5). This is because the mother's share, had she existed, would have been one-fourth (1/4); thus, her share is calculated as one share added to the other four existing shares, resulting in five total shares, so the bequest is one-fifth. This method of proportion is to be applied accordingly. This ruling, where the legatee receives one-fourth in the case of two sons and a bequest equal to a third heir's share, is the position held by the majority of scholars, including Al-Sha'bi, Al-Nakha'i, Al-Thawri, Al-Shafi'i, and the People of Opinion (Ashab al-Ra'y).