What a man does on making an error in voluntary prayer

Al-Sha'bi and Sa'id bin Jubayr said: There are prostrations of forgetfulness in voluntary prayer.

Al-Hasan held that the prostrations of forgetfulness apply in voluntary prayer.

Sa'id bin al-Musayyib said: Just as there are prostrations of forgetfulness in obligatory prayer, so there are in voluntary prayer too.

Ibn Awn says: I asked Muhammad whether doubt (wahm) is taken into account in voluntary prayer. He said: I do not know where its place is. I said: In the case of doubt in a voluntary prayer, should the two prostrations of forgetfulness be performed? He said: Do you consider voluntary prayer to be like the obligatory prayers? If such a thing happened to me, I would not perform the prostration of forgetfulness.

Qatadah did not take doubt (wahm) into account in voluntary prayer.