Hadith: The Prophet (may Allah's peace and blessings be upon him) entered the mosque and then a man came in and prayed. After that, he came and greeted the Prophet (may Allah's peace and blessings be upon him), who said to him: Go back and pray, for you have not prayed

عن أبي هُرَيْرَةَ رضي الله عنه «أنَّ النبي صلى الله عليه وسلم دخل المسجد، فدخل رجل فصلَّى، ثم جاء فسلَّم على النبي صلى الله عليه وسلم فقال: ارجع فصلِّ، فإنك لم تُصَلِّ، فرجع فصلَّى كما صلَّى، ثم جاء فسلَّم على النبي -صلى الله عليه وسلَّم- فقال: ارجع فصلِّ، فإنك لم تُصَلِّ -ثلاثا- فقال: والذي بعثك بالحق لا أُحْسِنُ غيره، فَعَلِّمْنِي، فقال: إذا قُمْتَ إلى الصلاة فَكَبِّرْ، ثم اقرأ ما تيسر من القرآن، ثم اركع حتى تَطْمَئِنَّ راكعا، ثم ارفع حتى تعتدل قائما، ثم اسجد حتى تَطْمَئِنَّ ساجدا، ثم ارفع حتى تطمئن جالسا، وافعل ذلك في صلاتك كلها».
[صحيح] - [متفق عليه]

Abu Hurayrah (may Allah be pleased with him) reported: The Prophet (may Allah's peace and blessings be upon him) entered the mosque, and then a man came in and prayed. After that, he came and greeted the Prophet (may Allah's peace and blessings be upon him) who said to him: "Go back and pray, for you have not prayed." The man went back and prayed as he had prayed before. Thereafter, he came to the Prophet (may Allah's peace and blessings be upon him) and greeted him. The Prophet (may Allah's peace and blessings be upon him) again said: "Go back and pray, for you have not prayed." When he had done that three times, the man said: "By the One Who sent you with the truth! I cannot do better than that. So teach me." The Prophet (may Allah's peace and blessings be upon him) said: 'When you go to pray, say Takbīr, then recite whatever you can of the Qur’an; then bow until you are at ease in bowing; then rise until you are standing up straight; then prostrate until you are at ease in prostration; and then sit up until you are at ease in sitting. Do that throughout your prayer."
[Authentic hadith] - [Narrated by Bukhari & Muslim]

Explanation

The Prophet (may Allah's peace and blessings be upon him) entered the mosque, and one of the Companions, Khallād ibn Rāfi‘, entered after him. He offered prayer in a brief and improper manner. Having finished his prayer, the man came to the Prophet (may Allah's peace and blessings be upon him) and greeted him. Returning his greeting, the Prophet (may Allah's peace and blessings be upon him) said to him: "Go back and pray, for you have not prayed." The man went back and prayed in the same manner. Then he came to the Prophet (may Allah's peace and blessings be upon him) who again said to him: "Go back and pray, for you have not prayed." He did the same three times, after which the man swore by Allah, the Almighty, saying: "By the One Who sent you with the truth! I cannot do anything better than that, so teach me." Once this man yearned for knowledge and was prepared to receive it, and it became apparent that he did not act out of forgetfulness, given the repeated instruction given to him, the Prophet (may Allah's peace and blessings be upon him) gave him the answer, saying: "When you stand up for prayer, say the Takbīr of Ihrām and recite whatever you can of the Qur’an after reciting Sūrat al-Fātihah. Then bow until you feel at ease in the posture of bowing, and lift your head from bowing until you stand up straight and become at ease in your standing. Then prostrate until you are at ease in the posture of prostration. Then lift your head from prostration and sit until you are at ease in sitting." You should repeat that throughout your prayer, except for the Takbīr of Ihrām, which is to be said in the first Rak‘ah only. The view that his statement "recite whatever you can of the Qur’an" means the recitation of Sūrat al-Fātihah at least is actually deduced from different versions of this Hadīth, as well as other pieces of evidence.