If a person omits the Qunoot of Witr because of forgetfulness or he does not recite out loud in a prayer where the recitation should done out loud, out of forgetfulness, he does not have to do the prostration of forgetfulness, but if he does prostrate there is nothing wrong with that. Doing the prostration of forgetfulness for omitting a Sunnah of prayer is permissible, but it is not obligatory. End quote.
Shaykh ‘Abd al-‘Azeez ibn Baaz (may Allah have mercy on him)