Fire bell in the night (Quotation)

Discussing the question of Missouri's admission to the Union, Thomas Jefferson wrote to John Holmes, "... but this momentous question, like a fire bell in the night, awakened and filled me with terror. I considered it at once as the knell of the Union. it is hushed indeed for the moment. but this is a reprieve only, not a final sentence."
- Jefferson to Holmes, April 22, 1820¹