Yusuf (may Allah have mercy on him) narrates from Sayyiduna Mu'awiyah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "Whoever forgets something in his prayer, let him perform two prostrations while sitting."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 16821