What should a person with a speech impediment do who believes the imamate of a person with a speech impediment, a latecomer, or an individual is invalid, if he is put forward to lead the prayer while he himself is a latecomer or an individual, or if he finds a second congregation and does not know how it started?

The preponderant view is the permissibility of praying behind a solitary person, the permissibility of a latecomer leading the prayer, and the permissibility of praying behind someone who has a speech impediment. If someone prays behind you, their prayer is valid, and nothing is required of you. If you find another congregation in the mosque, pray with them, and your prayer is valid even if it turns out that the imam was a latecomer or started his prayer alone. If the imam does something that the follower deems forbidden, but where there is room for scholarly discretion (ijtihad), the follower's prayer behind him is valid. The point of contention in this issue is if the follower becomes aware of it while praying; however, if they become aware after concluding their prayer, there is no need to repeat it. Praying behind someone who differs in subsidiary matters (furu') is permissible and does not invalidate the prayer of either the imam or the follower.