3 yo and pooping in diaper still

[playfelt]

If he knows that he needs to poop then he is old enough to do it in the toilet whether he likes it or not. We don't always get to do the comfortable thing and like it or not using the toilet is one of those rights of passage we just have to do. No more eating with the fingers - use a spoon, no more sucking on a bottle - here's a cup, no more soothers period..... the list goes on. You reach a point of being aware of bodily need then you take care of it appropriately - in the toilet.

If he is feeling that desparate then it is right at the edge and chances of him being able to hold it in for much longer are not likely so I would put him on the potty and then tell him bed after too.