Repeat all of it as it is void.

If i prayed my Isha and witr prayer before Isha time (20 minutes before) due to forgetfulness (thinking isha time has started), then what to do?

Prayer | February 13, 2014 8:31 pm
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Can I read dua from book “hisnul Muslim” during prayer before tasleem?because I have not memorised yet..As if we read from book then our hands were not in a position as they should be in before tasleem
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If one comes to the masjid late and prays 2 rakaat and the salah begins and everybody starts getting ready for congregational prayer and he still hasn’t finished tahyat al masjid should he stop his salah and pray with them or should he continue until he is done with the two rak’aat?