Is it permissible to test people's beliefs with specific questions such as, "Where is Allah?" and judge them based on the answer, and what is the evidence for that? And if it is not permissible, what is the advice for one who has fallen into this?

"Whoever is born and lives among Muslims, and outwardly professes monotheism, is to be considered a Muslim. There is no need to test their creed unless there is a specific need, such as teaching religious studies. This is supported by the hadith of the slave girl and a teacher's questioning of his students. The default is not to accuse a Muslim or doubt their faith without cause. The guidance of the Prophet (peace be upon him) and his companions was to first invite people to monotheism and accept those who affirmed it, without conditioning it upon their knowledge of the detailed intricacies of creed. Nevertheless, creed must be taught, and communities should be invited to it."