What is the ruling regarding a worshipper who starts praying alone, completes one rak'ah, and then joins the Imam, intending to follow him?
Chapter on the Two Prostrations of Forgetfulness
Al-Mughni
Book of Prayer
Primary text
If a worshipper starts alone, completes one unit (rak'ah), then joins the Imam, the juristic consequence regarding forgetfulness (suhū) depends on the interpretation of whether their respective errors are of the same 'kind' (jins). If the location of their required prostrations of forgetfulness are the same, they are considered one kind according to one view. If the kinds are differentiated by addition or subtraction, they may be considered two kinds.
Supporting text
If the worshipper joins a traveler after completing one rak'ah of a four-rak'ah prayer, and the Imam then concludes the prayer while the follower rises to complete the remaining units, the follower has been a follower in the middle of the prayer and alone at its beginning and end. If forgetfulness occurs in all parts, the ruling on whether the required prostrations constitute one or two kinds depends on whether the required prostration locations for the parts of the prayer are unified or different.