A: All praise be to Allah Alone, and peace and blessings be upon His Messenger, and his family and Companions.
If you have performed Wudu’, your basic state is Taharah (state of purity), so do not pay attention to these doubts and Waswasah (insinuating or obsessive thoughts), because they come from Satan. Yes, if you are truly certain that something has come out after you have done Wudu’, in this case Wudu’ becomes nullified and you should perform it again. As regards your feeling during prayer that there is some urine left in the penis, you have to keep your mind off this thought and act according to the basic state of Taharah in which you are. There is no need to examine yourself after this, for this reinforces the doubt and Waswasah you have. May Allah keep you safe from that.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.