“Even though I am careful not to share the mysteries, I feel that this is something I am permitted to reveal..This was something Rabbi Isaac had received directly from those who heard it from the mouth of the Vilna Gaon, who said, shortly before his passing:
“'When you hear that the Russians have invaded Crimea, you will know that the bells of Redemption have begun to ring. When you hear that the Russians have reached Constantinople (Istanbul, Turkey, as it is called today), you can already don Sabbath clothes and await the appearance of Moshiach.'
“Last week the Russians invaded Crimea and the world slept… According to our tradition from the Vilna Gaon, this is a sign of impending redemption … Perhaps what the Gaon meant by 'bells of the redemption' is like a bell that signals the arrival of someone or something.”
Adapted for easier understanding for readers of all level of familiarity with the tradition from the presentation and translation of the teaching in English by Rabbi Pinchos Lipschutz
An article in Hebrew on the Purim sermon can be found here.
Update: The version recorded in the writings of the Vilna Gaon's students' is as follows:
When the Russian ships cross the Dardanelles, it is already time to don Sabbath garments
היא כי כאשר יעברו ציים רוסיים במיצרי הדרדנלים, אפשר כבר ללבוש בגדי שבת...