Musannaf Ibn Abi Shaybah 4501 — What a man does on making an error

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.