This hymn is used for Sext on Sundays and Weekdays throughout the year in the Extraordinary Form of the Roman Breviary and the Ordinary Form.
This is the text of the hymn as it appears in Hymns Ancient and Modern (1867):
O God of Truth, O Lord of might,
Who orderest time and change aright,
Brightening the morn with golden gleams,
Kindling the noon-day’s fiery beams;
Quench Thou in us the flames of strife,
From passion’s heat preserve our life,
Our bodies keep from perils free,
And give our souls true peace in Thee.
Almighty Father, hear our cry
Through Jesus Christ our Lord most High,
Who with the Holy Ghost and Thee
Doth live and reign eternally. Amen.
Words: Attr. St. Ambrose, 4th C.; tr. John Mason Neale, 1852.
Tune: “Angels (Song 34)” Orlando Gibbons, 1623.
The original Latin text of this hymn may be found here.