Dr. Muzammil Siddiqi, President of the Fiqh Council of North America, states the following: It is permissible to repeat one verse several times and also the same Surah for the purpose of reflection and remembrance of Allah. But this is only if you are praying by yourself. If you are an Imam then you should not repeat the Surah. Also, if one is praying in congregation behind another Imam, then you follow the reading of the Imam.