Jami` at-Tirmidhi 303

Abu Hurairah narrated:"Allah's Messenger entered the Masjid, and a man entered and offered Salat. Then he came to give Salam to the Propet. He returned the Salam to him and said: 'Go back and perform Salat, for indeed you have not prayed.' So the man returned to pray as he had prayed. Then he came to give Salam to the Prophet. He returned Salam to him, then [Allah's Messenger] said: 'Go back and perform Salat, for indeed you have not prayed' until he had done that three times. So the man said to him: 'By the One who sent you with the Truth, I do not know any better than this, so teach me.' So he said [to him]: 'When you stand for Salat then say the Takbir, then recite what is easy for you of the Quran. Then bow until you are at rest while bowing, then rise up until you are at rest sitting. Do that in all of your Salat