From the Prologue from Ochrid:
The Commemoration of the Icon of the All-Holy Birth-Giver of God,
of the town of Vladimir
When the Tartar King Ahmet besieged Moscow, Prince John Vasillievitch set out with an army to defend the city. Even though the army of Prince John was smaller in number and weaker than the Tartar army, nevertheless, it emerged victorious. All at once, an indescribable fear overcame the Tartars and they became confused and fled. Everyone ascribed this unexpected success to the icon of the All-Holy Birth-giver of God before whom the Russian people prayed for salvation from the Tartars. As a result of this, June 23 was designated in Russia for the commemoration of this miracle.
Most Holy Theotokos, pray for us!