Is the Fajr prayer valid if one of the worshippers alerted the Imam that he had prostrated only once in the first rak'ah, even though he had prostrated twice, and so the Imam returned and prostrated once more, then completed the prayer and performed the prostrations of forgetfulness (sujood as-sahw)?

Scholars have differed regarding whether the Imam should heed the warning of a single worshipper in case of forgetfulness (sahw). Some hold that he should, while others do not. Abu Hanifa and Ishaq believe it is necessary to heed it, whereas Malik and Ahmad hold that the Imam should not heed the word of a single worshipper, but rather that of more than one. Ibn Qudamah argued that the Prophet, peace and blessings be upon him, did not heed the word of Dhul-Yadain alone. We hope that the prayer is valid as long as the Imam's action conforms to the opinion of some scholars, and usually the Imam does not heed the warning of a single worshipper unless he believes him to be truthful.