Answered by Shaykh Faraz Rabbani
While leading Zuhr salah I forgot to recite surah after Fateha in second rakat. Then I recited the surah in third rakat and performed prostration of forgetfulness (sajda sahw). Was it correct or do I have to repeat salah and let others know, who were followers?

Walaikum assalam wa rahmatullah,
What you did was correct:
Reciting a sura or at least the extent of three short verses of the Qur’an after the Fatiha is necessary (wajib) in prayer. Leaving a necessary (wajib) action does not invalidate the prayer; when done forgetfully, one’s error must be rectified by performing forgetfulness prostrations.
For details, search for relevant terms in the Hanafi Fiqh section at www.sunnipath.com
And Allah alone gives success.
Wassalam,
Faraz Rabbani