From https://lithub.com/when-picasso-saved-matisses-paintings-from-the-nazis/
The first Nazi official to visit Picasso during the war became part of an often-told story that may be apocryphal, but which was nonetheless related by Alfred Barr, Matisse’s first biographer. Not long after the conquest [of France], so the story goes, Otto Abetz, the infamous, though cultivated, German agent, called on Picasso. Picasso received him coldly, refused his offer of fuel, and showed him the door. On his way out of the studio Abetz noticed a photograph of Guernica. “Ah, Monsieur Picasso,” he said, adjusting his monocle, “so it was you who did that.”
“No,” replied Picasso as he closed the door, “you did.”
Related WITW Posts: Guernica The Art of Picasso: War and Peace