ANSWER:

Yes, only the 4 rakahs of Isha are mandatory. 

Kindly refer to the following link(s):

I want to know if the 4 rakats fard is the only mandatory rakat to pray and the other rakats are optional for Isha salah. I want to know if I am allowed to pray 3 rakats witr after praying 4 rakat fard for Isha salah.

Prayer | February 15, 2018 4:33 pm
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I got a question about reciting quran during my salah. I am learing some surahs but do i have to recite the whole surah or can i stop anywhere i want.
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Sheikh if a man or a woman sneeze during the khotba of jumuaa can he say elhamdulillah and how about the others can they tell him yarhamuka Allah ? Thank you very much.