Performing one Sujud only in the last Rak`ah then performing Sujud-ul-Sahw when remembering

Q 4: An Imam (the one who leads congregational Prayer) offered one Sujud (Prostration) in the last Rak‘ah (unit of Prayer) of a four-Rak‘ah Salah (Prayer consisting of four units). After he had said the Taslim (salutation of peace ending the Prayer), the Ma’mums (persons being led by an Imam in Prayer) drew his attention to his mistake, so he performed one Sujud only of Sujud-ul-Sahw (Prostration of Forgetfulness) and said that it compensated for what he had missed. He did not perform two Sujud? Was his Salah correct? A: If someone forgets to perform one of the two Sujud in the last Rak‘ah of a Salah and remembers it after saying the Taslim, and the time between the two actions (the missing and the remembering) is not long, they should perform Sujud, recite the final Tashahhud (a recitation in the sitting position in the second/last unit of Prayer), say the Taslim, and then perform the two Sujud of Sujud-ul-Sahw. There is nothing wrong if they perform them before saying the Taslim. However, if the time between the two actions is long, they should repeat the whole Salah from the beginning. Therefore, the Salah of the Imam was not correct, because he did not do what was required of him. Both the Imam and the congregation who prayed behind him should repeat this Salah. (Part No. 6; Page No. 18

A: If someone forgets to perform one of the two Sujud in the last Rak‘ah of a Salah and remembers it after saying the Taslim, and the time between the two actions (the missing and the remembering) is not long, they should perform Sujud, recite the final Tashahhud (a recitation in the sitting position in the second/last unit of Prayer), say the Taslim, and then perform the two Sujud of Sujud-ul-Sahw. There is nothing wrong if they perform them before saying the Taslim. However, if the time between the two actions is long, they should repeat the whole Salah from the beginning. Therefore, the Salah of the Imam was not correct, because he did not do what was required of him. Both the Imam and the congregation who prayed behind him should repeat this Salah. (Part No. 6; Page No. 18) May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.