The Synaxis of the Archangel Gabriel is celebrated on the day after the Annunciation, and a second time on July 13. It was instituted in the ninth century, perhaps to celebrate the dedication of a church at Constantinople. Originally, the Feast was observed on October 16 (Juan Mateos, LE TYPIKON DE LA GRANDE EGLISE).
An account of the Holy Archangel Gabriel is found under March 26 and November 8.
Troparion - Tone 4
Gabriel, commander of the heavenly hosts,
we who are unworthy beseech you,
by your prayers encompass us beneath the wings of your immaterial glory,
and faithfully faithfully preserve us who fall down and cry to you:
"Deliver us from all harm, for you are the commander of the powers on high!"
Kontakion - Tone 2
You look upon God's glory in heaven,
and bring grace from on high to earth,
wise Gabriel, leader of angels,
minister of God's glory, and divine defender of the world!
Save and preserve those who cry to you:
"Be our defense, so that no one can be against us!"