In what movie where 250 extras hired for a prison escape scene, when in fact 253 prisoners played in the scene, three who had escaped from a nearby mental ward?

The film is Exodus (1960)

"250 extras were hired to play escaping prisoners at the old prison in Acre. However, 253 people were counted as escaping, those three extra escapees were actual escaped inmates from a mental ward near the set."

link to IMBd

yup! I remember I knew this when I first watched exodus, so me and my sister tried to guess who was the guys were. It was a ton of fun!