If your baby is sound asleep and they have pooped their diaper there's no need to wake the baby up to change his diaper.
The baby can safely sleep overnight in a pooped diaper unless it is really runny and leaking out of the diaper then it would be a good idea to change it but otherwise just let him sleep.
To keep your baby or toddler dry, happy and comfortable you should check the babies diaper for wetness or poop every 1 to 2 hours.
Sometimes a baby or toddler may need a diaper change after an hour while other times they may not need a diaper change until 2 or 3 hours later.
It all depends on the baby.
Newborns will usually use 10 to 12 diapers per day while an older baby may use only 5 or 6 diapers per day.
As they get older they usually use less diapers per day and wet less often.
By the time the child gets to 2 or 3 years old they may only need 4 to 5 diapers per day and will usually wet after 2 to 3 hours.
If they drink more liquids during the day then they will wet more often but as long as you change the diaper every 3 hours or when it gets wet enough then you're doing okay.
If the kid has pooped the diaper then change it as soon as you notice.
However if the baby or toddler is asleep and pooped in their diaper then just leave it until morning as there's no need to wake the baby at night to change their poop diaper.