Preferability to perform Sujud-ul-Sahw before Taslim
We do not know of any evidence for this method, and none of the reliable scholars said that; therefore, it is not lawful to state or circulate it. According to the Sunnah (whatever is reported from the Prophet), you should say the Taslim twice. As for
Sujud-ul-Sahw (Prostration of Forgetfulness) it is preferable that it be performed before the Taslim, unless one ends the Salah by saying the Taslim but there remains one or more Rak‘ahs missing or one doubts having completed or omitted some part of the Salah and builds on what is more likely to have occurred; in these two cases it is better that after the Taslim Sujud-ul-Sahw is performed, followed by Taslim again, said twice (one to the right and one to the left). (Part No. 6; Page No. 43) May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.