Praying Four Rak‘as When Repeating Maghrib and Witr

Question

I have seen in some books that if sajda al-sahw (the prostration of forgetfulness) became wajib in Maghrib or Witr and [the person] forgot to perform it, then when repeating it (i‘ada) he should pray a full 4 rak‘as. Is there any basis for this, or is it merely one of the errors of the common people?

Answer

If this is in some book, its rationale would be as follows: by omitting a wajib, sajda al-sahw becomes necessary (lazim), while the fard is discharged. If sajda al-sahw was performed, the deficiency is made good; otherwise repetition (i‘ada) within the time is necessary (lazim)

Source: Fatawa Mahmudiyya

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