Touching a Very Young Girl with Lust

Question: While fondling my wife in bed one night, my hand fell on to the fingers of the four to five year old daughter sleeping with her. What is the ruling?

Answer: Because the child in question is small and not capable of being sexually aroused, there will be no prohibition taking place in terms of marriage." And Allaah knows best what is most correct.

Fatawa Rahimiyyah vol.3