My wife has always been a heavy sleeper. Occasionally while she slept and I lay awake, I would caress her body (we slept in the nude before we had children and all the interruptions that would bring one), enjoying the lovely texture of her warm skin and sensuous curves.
I would cup and hold her breasts, softly tweaking her nipples until they stiffened into their own miniature erections. Sensing her nocturnal arousal (and my own), my hands would drift down her body until they touched her curly-haired pubes. For the next several minutes, I would continue to just caress the area, letting my fingers just glide lighly across her slit. Eventually, I would feel her moistness, which signalled to me she was physically responding to my touching (but still quite asleep).
With her natural lubrication, it was easy for me to slip my finger into her warm wet folds and gently penetrate her pussy, making sure to press my finger and palm against her hood, putting friction on her tiny, but erect clit.
I could tell her arousal was intensifying when she unconsciously would open her legs and begin to breathe in a more laboured manner. On those times she was sleeping on her side, I had the added pleasure of stimulating her anus (which she has always enjoyed when awake!).
Eventually, I would feel my wife's body reach that point of no return and the muscles of her pussy would clench my finger as her thighs would clench my hand. Sometimes she would moan softly and stay asleep. Sometimes she would awake with a bewildered, but pleasing tone in her voice as she asked what happened. When I told her, she would giggle and then reward my efforts.