Musannaf Ibn Abi Shayba 3:582

Abu Usama narrated to us, he said: Ubaydullah ibn Umar narrated to us, from Sa'id ibn Abi Sa'id, from Abu Hurayrah, that a man entered the mosque and prayed, while the Messenger of Allah (may Allah bless him and grant him peace) was in a corner of the mosque. He came and greeted him, so he said: "And upon you be peace. Go back and pray, for you have not prayed yet." So he went back and greeted him. He said: "Go back, for you have not prayed yet." He said on the third time: "Teach me, O Messenger of Allah." He said: "When you stand for prayer, perform the ablution thoroughly, then face the Qibla, then say the Takbir, then recite what is easy for you of the Quran. Then bow until you are at ease while bowing, then rise until you are standing upright, then prostrate until you are at ease while prostrating, then rise until you are sitting upright—or he said: sitting—then do that in all of your prayer."