What is the ruling on prepaying Zakah for one hundred sheep by paying one sheep, if one hundred lambs are born, the mothers die, and the Hawl passes over the lambs?

Primary text

If one sheep is prepaid for one hundred sheep, and one hundred lambs are subsequently born while the mothers perish and the Hawl passes over the lambs, the prepaid sheep suffices for them. If only half the flock gives birth, and half the mothers die, leaving half young and half old stock, if the first position is adopted, the prepaid offering suffices for both groups. The second position holds that Zakah is due on the fifty surviving lambs as they constitute a Nisab whose Zakah has not been paid. However, nothing is due on fifteen surviving heifers, as they have not reached a Nisab, their Zakah obligation being predicated upon their mothers for whom Zakah was prepaid.