What Is the Ruling of Praying behind the Masbuq?
Taking the Masbuq as Imam in Prayer
If a person joins the congregational Prayer in last rak`ahs and then after Imam finishes the prayer he stands up, he is considered masbuq now. Then, someone starts a congregational behind him, making him Imam. Is it correct that a masbuq becomeس the Imam in the second congregation?
In the name of Allah, We praise Him, seek His help and ask for His forgiveness. Whoever Allah guides none can misguide, and whoever He allows to fall astray, none can guide them aright.
Masbuq or latecomer is the person who joins the congregational prayer after the ruku` (bowing) in the first rak`ah. This is a controversial issue among the jurists, some of them like the Hanafi and Maliki schools are of the view that it is not permissible to pray behind the masbuq imam and thus prayer of the muqtadi (ma’mum) will be invalid.
On the other hand, Shafi`i, Hanbali and Imam Ibn Taimiyah are of the view that it is permissible for a person to pray behind the masbuq and such prayer will be valid. This the correct view. Sa`id Al-Khudri (may Allah be pleased with him) narrated that the Messenger of Allah (peace be upon him) saw a person praying alone. He said: “Is there any man who may do good with this (man) and pray along with him.” (Authenticated by Al-Albani)
Source: Fatwa of Dr. Abdul-Karim Ibn Abdullah Al-Khudir, member of The Council of Senior Scholars is the Kingdom of Saudi Arabia.Soucre Link