What is the ruling when one forgets a specific prayer from a day and night but does not know which one it was?

Primary text

If a person forgets a single prayer from a day, not knowing which specific prayer it was, they must make up both the prayer of that day and the prayer of the following night (a total of one day and one night's worth of prayers). Imam Ahmad explicitly stated this, and it is the position of the majority of scholars. This ruling is necessitated because specification (Ta'yeen) is a condition for the validity of an obligatory prayer, and the only means to fulfill this requirement here is by repeating the five prayers of the day and night.