In the narration from Sayyiduna Abdullah bin Ja'far and Sayyiduna Muawiyah (may Allah be pleased with them both) from the Prophet (peace and blessings be upon him), it is stated: "Whoever has doubt in his prayer should perform two prostrations while sitting in Tashahhud." (The author of the book states:) I have mentioned these ahadith with their chains of narration in Kitab al-Kabir. And these words are brief and not detailed.
Hadith Referenceصحيح ابن خزيمه / جماع أبواب السهو فى الصلاة / 1022