"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."
أَنَّ النَّبِيَّ ﷺ صَلَّى الظُّهْرَ خَمْسًا فَقِيلَ لَهُ أَزِيدَ فِي الصَّلاَةِ فَسَجَدَ سَجْدَتَيْنِ بَعْدَ مَا سَلَّمَ