ANSWER:

If such a person was a well known atheist and that was public, this is permissible.

But if it was concealed and no one knew about it, this is not permissible. 

Sheikh, is it permissible for a person to tell people that “I was also an atheist but then ALLAH guided me to the straight path” while giving dawah to non muslims or does this fall under the category of exposing sins.

Halal/Haram Matters, Sins | February 20, 2022 7:02 pm
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When i knock on my moms room door, she sometimes doesn’t say “come in” or , she also says “yes?” and I know this gives me permission to go into her room, is it okay for me to go into her room even if she doesn’t say specifically “come in” ?