What is required if one discovers an omission of a mandatory part of ablution after praying subsequent prayers?
Chapter on the Obligation of Purification
Al-Mughni
Book of Purification
Primary text
If one performs ablution, prays Dhuhr, subsequently invalidates purity, performs ablution again, and prays Asr, and then discovers they omitted wiping the head or another obligatory part in one of the two ablutions, both ablutions and both prayers must be repeated. This is because the invalidity of one of the two prayers is certain, even if the specific prayer is unknown. Similarly, if one omits an obligatory part in one of the five daily ablutions without knowing which one, they must repeat the ablution and all five prayers. This is analogous to forgetting one of the five prayers on a day when the specific one is unknown.
Supporting text
If the second ablution was a renewal not necessitated by a state of impurity, and renewal is deemed not to remove impurity, the initial prayer remains invalid because the renewal is ineffective. If renewal is considered to remove impurity, only the initial prayer needs repetition: if the first ablution was valid, all subsequent prayers are valid because the purity was maintained and not nullified by the renewal; if the first ablution was invalid, the impurity was subsequently removed by the renewal.