It is a major sin and your will be punished for it in hell fire for sometime until Allah wills that you get out, if you were able to fast and did not!

For my case, will it be sins of shirk or sins of intercourse during day of Ramadan if i did not pay my expiation intentionally.

Fasting | August 4, 2015 2:35 am
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Actually before i broke my fast, i have the thoughts that i am worshipping my desires and wife if i broke my fast and have intercourse with her yet i still went ahead and did it. If i repented but did not even try to fast back 14 months of 7 days that i purposely skipped and die this way. Will my sins be forgiven? If not, is it shirk or sins of breaking fast?
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If you broke your fast thinking it was time (but were not certain) and you did not find out afterwards that you were wrong, do you have to make up for that day? Apparently, many scholars have said that it is not necessary, due to the fact that you did not know whether you broke your fast too early or not (you’re having doubts with no certainty), but I am wondering if that is the correct opinion.