I have some urinary incontinence. I use pads to alleviate the problem, but they are very absorbent. According to a hadith, if one sees signs of wetness upon waking up, one must perform ghusl (shower taken in case of major ritual impurity). I usually do not do so, but if I do go to sleep wearing the pads, then even if I had a wet dream, there would be no sign of wetness left. Thus I would not know whether I had had a wet dream or not. In such a case, would it be obligatory for me to perform ghusl?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ʻalayhi wa sallam, is His slave and Messenger. 

We fear that your question arises from waswaas (obsessive whisperings). Semen is known to be a thick white fluid. It is quite unlikely that you would see a wet dream and wake up without finding any traces of semen on your body or clothes or on that pad. Moreover, when semen dries, it leaves recognizable traces and smells like date-palm pollen or dough, as has been underlined by Fiqh scholars. Please refer to fatwa 82518.

Hence, we advise you to ignore such whisperings and completely disregard them. You are not obliged to perform ghusl unless you know with certainty, beyond any doubt, that semen was discharged, and you need to be so certain that you would swear to it. Without the element of absolute certainty, the basic principle is that you are ritually pure and you are not liable for anything nor obliged to perform ghusl.

Allaah knows best.