There are two orientations regarding this matter:
Some scholars argue that if the follower knows about a forgetfulness in an obligatory act that the Imam is unaware of, the follower should not perform the prostration of forgetfulness individually. This is based on the hadith where the Prophet, peace be upon him, said: “The Imam was appointed to be followed.” (Reported by Al-Bukhari and Muslim) Since the Imam did not perform the prostration, the follower should not do so either.
Others, however, argue that the follower should perform the prostration of forgetfulness individually. They believe that once the Imam concludes the act with the closing salutation (tasleem), the follower’s adherence to the Imam’s actions ceases, and there is no longer an obligation to strictly follow the Imam. This is while maintaining the necessity of rectifying the prayer with the prostration of forgetfulness.
And Allah knows best.
Fatwa by Dr. Khālid Naṣr