Ruling on prostrating for forgetting Qunoot or forgetting to recite out loud
Question

                Do I have to do the prostration of forgetfulness when I forget to say the du’aa’ of Witr? Should I do the prostration of forgetfulness if I do not recite out loud at times when the recitation should be out loud, because I forgot?.
Praise be to Allah.
      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)