Lily,James and Azkaban.

[wapp13]

No: HPFGUIDX 112706

"girl_next_door704" wrote:       
 	                                                             
<<In Book Five, Aunt Petunia says she knows of the Dementors and about the wizards' prison Azkaban because she had once heard James Potter talking about it with Lily.>>

Actually she didn't mention James Potter at all.  She said she heard
"that awful boy" telling Lily about them.  Debates exist on this site 
about whether the awful boy could in fact be someone else.