Waki' bin al-Jarrah وكيع بن الجراح · The Book of Forgetfulness (In Prayer)

The Prophet (ﷺ) said: "If one of you does not know whether he prayed three or four (rak'ahs), let him pray a rak'ah then prostrate twice after that when he is sitting. Then if he prayed five (rak'ahs), they (the two prostrations) will make his prayer even-numbered, and if he had prayed four, they will annoy and humiliate the shaitan."

"The Messenger of Allah (ﷺ) addressed us and taught us our Sunnahs and our prayer. He said: 'When you stand for the prayer, make your rows straight, then let one of you lead the others. When he says the takbir, then say the takbir; when he says : "Wa lad-dallin" then say "Amin" and Allah (SWT) will answer you. Then when he says the takbir and bows, then say the takbir and bow, for the Imam bows before you and…