If One Prays Five Rak'ah Sunan Abi Dawud 1019
Translation
‘Abd Allah (b. Mas’ud) said
The Messenger of Allah (ﷺ) prayed the Zuhr prayer five (rak'ahs). It was said to him: 'Has something been added to the prayer?' He said: 'What is that?' They said: 'You prayed five.' So he performed two prostrations after giving the salutation.