"The third hour was made rich with grace..."

Holy Pentecost (source)

  
The third hour was made rich with grace,
That it might indicate the worship of
Three Persons in singleness of authority;
But now on the one Sovereign of days,
Son, Father, Spirit, blessed are you.
-Second (Iambic) Canon of Pentecost
  
(source)
  

Through the prayers of our Holy Fathers, Lord Jesus Christ our God, have mercy on us and save us! Amen!