It is valid due to your ignorance.

I just found out from islamqa.info [1] that saying “رب اغفرلي” between two prostrations is obligatory (I don’t recite it) ,does that mean all of my ten years worth of prayers are invalid?

Prayer | August 16, 2016 3:12 am
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In jumuah khutba when Prophet.s.a.w’s name comes, can we say his name or darood?
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I went to the masjid and intentionally waited about 1second so that the imam goes to ruku.when he went to ruku,I joined.I did this delay because I know that I cannot recite fatiha in 1second.Should I repeat the prayer?