Board Thread:Questions and Answers/@comment-25958552-20161104191552/@comment-27701762-20161104192832

That dialogue occurs if you sleep in the bed again after asking Toriel how to exit the Ruins. It is when you sleep in the guest bed (the bed you sleep in the first time), not Toriel's bed (since she has her own bed in her own room). The trigger is noted on the Toriel's Home page. I'm not sure what else you need explained.