The World Federation One Stop Fiqh

Ruling 1526

If a person is hired to, for example, perform the prayers of a deceased person within the period of one year, and if he dies before the end of one year, then another person must be hired to perform the prayers that are known not to have been performed [by the previous hired person]. And if it is deemed probable that the hired person did not perform them, then based on obligatory precaution another person must still be hired.