A man entered the mosque and prayed, then came to the Prophet ﷺ and greeted him. The Prophet ﷺ returned the greeting and said, "Go back and pray, for you have not prayed."So he went back and prayed again, and this happened three times.The man then said, "By the One who sent you with the truth, I cannot do better than this, so teach me."The Prophet ﷺ said, "When you stand for prayer, say the takbir, then recite whatever is easy for you from the Quran. Then bow until you are at ease in bowing, then rise until you are standing upright, then prostrate until you are at ease in prostration, then rise until you are at ease sitting. Then do that throughout your entire prayer."
حدثنا يحيى عن عبيد الله قال حدثني سعيد بن أبي سعيد عن أبيه
دخل رجل المسجد فصلى ثم جاء إلى النبي ﷺ فسلم فرد عليه السلام وقال ارجع فصل فإنك لم تصل فرجع ففعل ذلك ثلاث مرات قال فقال والذي بعثك بالحق ما أحسن غير هذا فعلمني قال إذا قمت إلى الصلاة فكبر ثم اقرأ ما تيسر معك من القرآن ثم اركع حتى تطمئن راكعا ثم ارفع حتى تعتدل قائما ثم اسجد حتى تطمئن ساجدا ثم ارفع حتى تطمئن جالسا ثم افعل ذلك في صلاتك كلها
Its isnad is sahih. Bukhari related it, 1/192-193, in the Book of Adhan, on the obligation of recitation for the imam and the one following him, with wording close to this, as did Muslim, 4/298, no. 397, in the Book of Prayer, on the obligation of reciting Fatihah, and Tirmidhi, 2/103, no. 1060, and Abdul-Razzaq, 2/370, no. 3739.