Where did St. Catherine of Siena say: “Preach the Truth as if you had a million voices. It is silence that kills the world.”?

Question

Where did St. Catherine of Siena say: “Preach the Truth as if you had a million voices. It is silence that kills the world.”?

^{quoted in this article}

Answer 1

It comes from Lettera 16, "A uno grande prelato" ("to a great prelate"):

Oimé, non più tacere! Gridate con centomiglia di lingue. Veggo che, per lo tacere, el mondo è guasto, la Sposa di Cristo è impalidita

^{O alas, be silent no more! Shout with a hundred thousand tongues. I see that, through silence, the world is broken, the Bride of Christ is impaled}