Imam finished 3 rakat for maghrib, and stood up for 4th by mistake

الاستفتاء

If Imam finished 3 rakat for maghrib, and stood up for 4th rakat by mistake, and one of the muqtadis gave him luqma as Subhan Allah to remind him or error. But he continues for the fourth rakat knowing that he made an error. He offered Sijda Sahu at end of fourth rakat. Muqtadis wanted him to repeat the salat, but he quoted Hadiths to support that there is no need to repeat. He wants quote of Hadith to prove that he has to repeat magrib salat. The argument is that he continued for the fourth rakat, even he was reminded by the muqtadi by saying Subhan Allah, he should have gone to Qaida immediately, and do sijda sahu to end the salat. Please respond with references. Jazakum Allah Khair. Wassalaam.

الجواب حامدا و مصلیا

If the referred Imam stood up for the fourth Raka’ath erroneously after performing the last sitting (Qa’da e Akheera), each person’s Salath would become valid by performing the Sajda e Sahw and repetition is not necessary. If the Imam had not performed the Qa’da e Akheera at the end of the third Raka’ath no one’s Salath would have become valid and it is necessary for all to repeat the Salath.