This is the Hail Holy Queen that the final prayer of the Rosary. It is also on of the four Marian antiphons with the Alma Redemptoris Mater, Ave Regina Caelorum and the Regina Coeli all of which are sung/prayed during compline or night prayers during the Liturgy of the Hours.
In case you don’t know it here it follows:
Hail, holy Queen, Mother of Mercy, our life, our sweetness and our hope. To thee do we cry, Poor banished children of Eve; To thee do we send up our sighs, Mourning and weeping in this valley of tears. Turn then, most gracious advocate, Thine eyes of mercy toward us; And after this our exile,
Show unto us the blessed fruit of thy womb, Jesus. O clement, O loving, O sweet Virgin Mary.
Pray for us, O holy Mother of God, that we may be made worthy of the promises of Christ.