You've already gotten the answer from a few ladies that indicates that your child's body/brain have not matured to the point that night-time dryness is happening, or even possible. I absolutely agree with them. I also have a four-year-old, and he is an extremely heavy sleeper and does not get the signals that he needs to pee.
I got to where I didn't want to pay for diapers any more, so before my husband and I go to bed each night, we get our boy up and take him to use the toilet. This usually occurs about three hours after our boy has fallen asleep. We call this little ritual "squeezing the boy". His sleep is not disturbed by this little outing to the potty, and in fact thinks it is funny the next morning when his daddy tells him about their squeezing conversations. DH will ask our son if he wants to go ride bikes, swimming, watch a movie, play marbles, shave the dog (just kidding on this one) or whatever, and our boy ALWAYS says NO. Then in the morning they have a big laugh about it. 99.9% of the nights we do not have an accident, and our boy isn't wearing diapers, or pull-ups, or plastic pants or anything that is uncomfortable. But just in case, we also use a waterproof mattress cover. We have two of the covers and two sheets so if he does have an accident, we don't have to wait around for the laundry.
Keep in mind that when his body and brain mature enough, you won't have any more accidents and you certainly won't have a traumatized child because you didn't make him clean up after himself, you didn't scold him, you didn't belittle him.
Actually, the idea of taking the child to the potty several hours later is not new, as my folks had to do it for me when I was a child, and I'm a 45!
Give it a try. And tell your husband what the ladies have said about the physiological development that keeps your boy from knowing/waking enough to pee at night.
Good luck.