You must stand up and complete the missing fourth Rakah and then offer two prostrations after Salam.

If you didn’t do that, your prayer is invalid as you have dropped a pillar of prayer and you must repeat it.

what will I do if I am praying isha where by I should pray 4 raka an I forget an pray 3 what should I do?

Prayer | June 28, 2015 12:01 am
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In our mosque 2 imams alternately conduct taraweeh and after 20 rakaths a new imam who was praying behind in the first row conducts witr. so if I go hone after 20 rakats will I get the reward of praying the entire night?
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As we pray taraweeh and witr in the masjid with imaam, i couldnt actually pray tahajjud after a small nap as i prayed witr with the imam. so can i have intention of praying taraweeh when the imam praying witr and after the last one rakah tashahudd can i complete it as a two rakkah taraweeh and go home and do the tahajjud and witr with my convinience?