What is the ruling on the prayer of one who prayed Jumu'ah behind an Imam who made a mistake in the first prostration, was alerted to it, then performed only one prostration of forgetfulness (Sajdat As-Sahw), and did not correct his mistake, knowing that he was ill?

It seems everyone acted without knowledge of the rulings concerning the prostration of forgetfulness (sujood as-sahw). The majority of jurists hold that it is not permissible for a mukallaf (accountable person) to undertake an action without knowing Allah's ruling on it. One who is ignorant of the Sharia rulings is like one who acts intentionally, unlike the forgetful person who is excused. Therefore, those who omitted the second prostration out of ignorance, their prayer is invalid because their ignorance is like intentional action. As for those who re-performed the Jumu'ah prayer as Dhuhr, they were correct.

A distinction is made between commanded acts (ma'muraat) and prohibited acts (manhiyaat). Ignorance and forgetfulness are excuses in the case of prohibitions but not in the case of commanded acts, because commanded acts are intended for the mukallaf's benefit and are only achieved through action.

According to the Shafi'is, everyone's prayer is valid because the prostration of forgetfulness is a Sunnah for them, not an obligation. However, the opinion of the majority is stronger and more cautious. Therefore, those who omitted the prostration and did not pray Dhuhr must make up the prayer to clear their conscience.