The story of Omar Ibn Al Khattab (radiAllahu anhu) burying his daughter alive, which even i used to quote, is a pure fabrication that is disproved by historical facts. Omar became Muslim in his twenties and already had 3 daughters amongst whom was Hafsa (ra) who would marry the Prophet (salAllahu alayhi wa salam). Of course even if the story were authentic, Islam expiates all sins before it, but history shows otherwise. There is also not a single authentic narration of this story what so ever. The only recorded narration is by a man named jaabir al jufee who is rejected and consider a liar and fabricator by consensus.
Taken from Omar Suleiman
I just though y'all should know (: