https://www.sefaria.org/Gittin.58a.8?lang=bi

There were four hundred synagogues in the city of Beitar, and in each and every one of them there were four hundred schoolteachers, and each and every one of these teachers had four hundred schoolchildren.

And when the enemy entered there, these schoolchildren stabbed them with their pens [beḥotreihen]. And when the enemy prevailed and caught them, they wrapped the children in their scrolls and lit them on fire.