´Abdullah bin Masud narrated:` "The Prophet (S) prayed five (Rakah) for Zuhr, so it was said to him: 'Has the prayer been added to, or have you merely forgotten?' So he (S) performed two prostrations after he had said the Salam."
Hadith ReferenceSunan at-Tirmidhi / The Book on As-Shw / Hadith: 392
Hadith Gradingالألبانی:صحيح، ابن ماجة (1205 و 1211 و 1212 و 1218)