Here is the first prayer for the Mass of 23 December, the last full day of Advent before the Vigil of Christmas. It is also Ember Saturday and the Roman Station is St. Peter’s Basilica.
Omnipotens sempiterne Deus,
nativitatem Filii tui secundum carnem
quaesumus, ut nobis indignis famulis tuis
misericordiam praestet Verbum,
quod ex Virgine Maria dignatum est caro fieri,
et habitare in nobis.
This is an ancient prayer from Rotulus 24 published with the Veronese Sacramentary.
Almightly eternal God,
we beseech you as we are discerning that
the Nativity of Your Son according to the flesh approaches,
that the Word grant mercy to us Your unworthy servants
for He deigned to be made flesh from the Virgin Mary
and the dwell amongst us.