I was doing the same thing until very recently. Now I know when you do wudhu as part of ghusl, then you do another wudhu at the sink after the shower. However, it was recently brought to my attention that apparently the angels are with us while we do wudhu before prayer and so we should have some clothing on, and not just underwear but some pants and a t-shirt for example, because the angels are present. Has anyone else heard of this? Jazak Allahu Khair.