In the case of a bequest concerning a slave's neck (ownership) and another's benefit (usufruct), upon whom does Zakat al-Fitr fall?

Primary text

If a slave is bequeathed such that one person receives the neck (ownership) and another receives the benefit (manfa'ah), and both accept, the Zakat al-Fitr is due from the owner of the neck because Zakat al-Fitr is obligated by the possession of the neck, not the benefit. This is evidenced by the fact that it is due even from one for whom there is no benefit.