Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) narrates about the Noble Prophet (peace and blessings be upon him): He led five rak'ahs in the Zuhr prayer. It was submitted to him: Has there been an addition in the prayer? He said: What has happened? The people said: You have led five rak'ahs. So the Noble Prophet (peace and blessings be upon him) performed two prostrations of forgetfulness (sajda sahw) after concluding the prayer with salam.
Hadith Referenceصحیح ابن حبان / كتاب الصلاة / 2682
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح: ق - انظر ما قبله.فضيلة الشيخ العلّامة شُعيب الأرناؤوطإسناده صحيح على شرطهما