What is the ruling on willing compensation for a slave to his *Umm Walad*?

Primary text

A bequest (*Wasiyyah*) bequeathing the substitute value of a slave to his *Umm Walad* is valid, even if the substitute value has not yet become obligatory, similar to bequeathing future fruit. The right to *Qasamah* in this scenario belongs to the heirs, as they stand in the place of the testator for establishing his rights. If the heirs swear the oath, the compensation is established for the *Umm Walad* through the bequest; if the heirs refuse to swear, she cannot swear herself.