Did Ibn Taymiyyah find anyone to agree with him regarding the absolute excusability of the ignorant and the mistaken, and is he therefore considered an outlier in both subsidiary matters and foundational principles, or does Al-Shanqiti’s agreement with him support him, and did the Salaf or the great imams support him in this, and is it understood from his saying that he validates the prayer of someone who prayed while forgetfully in a state of major ritual impurity (janabah)?

Shaykh al-Islam Ibn Taymiyyah was not an outlier in his view of excusing ignorance. He based this on textual evidence from divine revelation, a position adopted by many scholars, such as Ibn Qudamah, al-Nawawi, Ibn Hazm, al-Suyuti, and al-Qarafi. They explicitly stated that whoever is a recent convert to Islam or grew up in a remote desert area far from Muslims, such that it is conceivable that the obligation of certain matters might be hidden from him, is not considered an apostate merely by denying them until he is informed. If he denies them after being informed, then he becomes an apostate. However, Shaykh al-Islam Ibn Taymiyyah did not validate the prayer of someone who prayed having forgotten that he was in a state of ritual impurity (janabah), because he held that ritual purity for major impurity is not waived by forgetfulness or ignorance. This is what Muslims have unanimously agreed upon, according to al-Nawawi.