There are probably more than a dozen Mubaahila's, I hadn't heard of this but found this. I'm not sure if this link will work for you, let me know if it doesn't I'll copy & paste it.
https://www.alislam.org/books/truth/challenge.html
https://www.alislam.org/books/truth/challenge.html
The story I posted is very popular in the region. Always it gets my interests to know how the religion reached in your hometown and other areas. Arrogance is the reason why such hate is grown up fast between the sects rather than looking for the truth. If you study deep about the 73 sects hadith, you will understand what I am talking about.
I don't know how you became Ahmadi, so I can't judge on you for that, however, if you look back to the history of the Ahmadiyaa community, you'll find plenty of mystery.
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