Is a conditional bequest valid when specifying distribution over time until death?

Primary text

A bequest stipulating that a portion (one-third) belongs to an individual, who is to receive a fixed monthly allowance (one hundred per month) until their death, is valid and executable according to the will of the testator. If the recipient dies and a surplus remains from that portion, the remainder reverts to the owner of the original principal (the remaining two-thirds). This ruling is conveyed from Ahmad via Hasan ibn Thawab, affirming the validity and enforcement of the bequest as commanded by the testator.