Matthew 24:22

And except those days had been shortened, no flesh would have been saved: but for the elect's sake those days shall be shortened.

This was fulfilled in the relatively short duration of the siege which lasted only five months. That some degree of mercy was granted "for the elect's sake" lends New Testament emphasis to the principle taught in the Old Testament to the effect that ten righteous persons would have prevented the overthrow of Sodom and Gomorrah and the cities of the plain.