The prayer is valid but  he will be sinful for his deed.

If a person is praying, but he has an intention in his mind that he will do a major sin afterwards, is his prayer nullified?

Sins | December 21, 2014 2:30 am
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What is the punishment from Allah to a women who commit adultery? Can she be forgiven if she repent to Allah? Is there any kaffara she must do to be forgiven?
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which sin is greater: disobeying parents or riba[interest]?