Answered by Shaykh Faraz Rabbani
Can we make sajdah sahw in a sunnah/nafl prayer? Or must we pray the salaat again?
Assalamu alaikum wa rahmatullah
Forgetfulness prostrations are necessary (wajib) to perform for leaving any of the necessary (wajib) actions of the prayer forgetfully. It is not performed for anything else–whether deliberate omission of necessary actions, or the omission of sunna actions, or the performance of something disliked.
Please see the following related SunniPath Answers (http://qa.sunnipath.com):
Jazakum Allah khayr.
And Allah alone gives success.
Faraz Rabbani