What is the ruling on the Imam prolonging the last prostration? Is it permissible to stop following the Imam and pray individually if the Imam prolongs [it]? Is one who objects to the Imam because of prolonging the last prostration sinful? Is the prayer valid if the worshipper says the tasleem four or six times, and must it be repeated?

There is no harm in the statement of whoever specifies that prolonging the last prostration is contrary to the Sunnah (definition). It is permissible for a congregant to leave the Imam due to an excuse. There is no evidence that Ibn Taymiyyah prolonged the last prostration until Fajr, and even if it occurred, it does not make it a Sunnah. If a worshiper doubts about the tasleem (salutation), he should perform it and does not make the prostration of forgetfulness because its place has passed. However, if he intentionally adds something, then the prostration of forgetfulness is due after the tasleem, and the prayer is not invalidated by intentionally omitting it.