Answered by Shaykh Sohail Hanif, SunniPath Academy Teacher
I had a dream in which I am sure not to have had resulted in ejaculation, but I did see on my undergarment a few drops of what seemed to be mathi, or wady, in the dream. When I woke up and checked my undergarment, there was no sign of mani or mathi or wathi as best as I could determine. I used the criteria of if there was a sign of wetness, if there was a slight coloration, if there was a clear border for a spot, or if there was harshness in the texture of the cotton. None of these signs were there. Do I make ghusl in this case? If not, should I assume that my undergarment is najis because there may have been mathi that evaporated (but there is no way I can determine if that occurred)?
In the Name of Allah, Most Merciful and Compassionate. May His abundant blessing and most perfect of peace be on His Beloved Prophet, the best of creation, and his family, companions and followers.
The scholars mention that if one sees a dream which would normally cause a wet dream but upon awakening one does not see any trace of any sort of emission then one assumes that nothing happened. So in your question, you would not be required to do a ghusl nor is your under garment impure.
The general rules related to wet dreams are summarized in the answer below.