Answered by Shaykh Faraz Rabbani
Is the obligation of forgetfulness prostration is different for different prayers (fard, wajib and nafl). Or it is the same for all the prayers? Because once some mistake took place in Taraweeh and after that somebody told that there was no need to make Sajda Sahaw because it was a Nafl prayer. Is that true or it depends on the mistake?
Walaikum assalam wa rahmatullah,
Forgetfulness prostration is due in any prayer in which one leaves out a necessary action forgetfully. [Imdad al-Fattah Sharh Nur al-Idah, Durr al-Mukhtar]