Having the trousers below the ankles is forbidden whether during prayers or outside of it. Therefore, if a person is sinning and keeping it below the ankles, he should at least fold it for praying.

I have a question to ask the Shaikh , the question is that i have seen some people who when enter the Masjid they fold there pants to make it above the ankle. So is it from the sunnah, should i do it too? because my pants are usually covering my ankles.