This is Two Women at a Window by Bartolomé Esteban Murillo.
When I lived in Washington I went to the NGA all the time and always made sure to see this painting. It's like the girls in the painting are looking back at you...
Super HQ version (17,385x20,855):
https://commons.wikimedia.org/wiki/File:Bartolom%C3%A9_Esteban_Perez_Murillo_014.jpg