1) Would you mind elaborating on the concept of retesting on the day of judgment?

2) Do you recommend any resources (articles, books) about this topic?

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1) We have hadiths that certain categories of people will be retested on the Day of Judgment. One hadith states Allah will speak to them and ask them: do you now have any doubts I exist and that I am your Lord? They will say no. The Allah will create a fire and command them to enter it. Those who enter it pass the test (of course they don’t get burned). Those who refuse fail their test. Some scholars believe this is symbolic and not to be taken literally (meaning Allah will retest them by giving them some command to fulfill).

2) I am not aware of English sources
But in Arabic in Behar al-Anwar Allammah Majlisi mentions some of those hadiths:

http://shiaonlinelibrary.com/الكتب/1436_بحار-الأنوار-العلامة-المجلسي-ج-٥/الصفحة_297