Can one pray behind a person who doesn’t have a fistful beard and also if you don’t have good thoughts/opinions on the person who leads the prayer?
It is makrūh tahriman (severely disliked) to pray behind a person who openly disregards a fardh or wājib, such an individual is termed a fāsiq in the books of fiqh.
A Muslim should have only good thoughts about his Muslim brother and many a bad or evil thought may be considered a sin as we know from the teachings of Qur’an and Sunnah. To avoid praying behind a Sunni who outwardly fulfils the conditions of imāmat (leading the prayer) without solid evidence of him being from the people of bidah or fisq is incorrect.
Allāh knows best.
Answered by Shaykh Naveed Jameel ash-Shaami