What is the ruling on a congregant who prayed Fajr behind an imam who prayed silently and did not correct his prayer after being alerted, justifying his action by not wanting to disturb the Quran reciter in the mosque, and is the imam considered ignorant of the rulings of prayer?

If the Imam omits vocalizing the recitation where it is required, the ruling on this issue is detailed in Fatwa No. 37998. It is not appropriate to judge an Imam as ignorant of the rulings of prayer based on a single issue, because the basic principle is that whoever's prayer is valid, their imamate is valid. Al-San'ani supported this with the actions of the Companions and their prayers behind oppressive Imams, as well as with the Hadith in Muslim that permits praying behind rulers who delay the prayer beyond its time, for if they had performed it on time, it would have been an obligatory duty.