36 Let not us, then, who are in Christ— that is, always in the lights cease from praying even during night. Thus the widow Anna, without intermission praying and watching, persevered in deserving well of God, as it is written in the I Gospel: “She departed not,” it says, “from the temple, serving with fastings and prayers night and day.” Let the Gentiles look to this, who! Are not yet enlightened, or the Jews who have remained in darkness by having forsaken the light.
Let us, beloved brethren, who are always in the light of the Lord, who remember and hold fast what by grace received we have begun to be, reckon night for day; let us believe that we always walk in the light, and let us not be hindered by the darkness which we have escaped. Let there be no failure of prayers in the hours of night— no idle and reckless waste of the occasions of prayer. New-created and newborn of the Spirit by the mercy of God, let us imitate what we shall one day be. Since in the kingdom we shall possess day alone, without intervention of night, let us so watch in the night as if in the daylight. Since we are to pray and give thanks to God for ever, let us not cease in this life also to pray and give thanks.
Source: The Treatises of Cyprian (New Advent)