Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings be upon him) prayed Zuhr with five rak'ahs. It was said to him (peace and blessings be upon him): O Prophet of Allah, has something been added to the prayer? So he (peace and blessings be upon him) gave the salam, then performed the two prostrations of uncertainty.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9805