29 Nor was it only in words, but in deeds also, that the Lord taught us to pray, Himself praying frequently and beseeching, and thus showing us, by the testimony of His example, what it behooved us to do, as it is written, “But Himself departed into a solitary place, and there prayed.” And again: “He went out into a mountain to pray, and continued all night in prayer to God.” But if He prayed who was without sin, how much more ought sinners to pray; and if He prayed continually, watching through the whole night in uninterrupted petitions, how much more ought we to watch nightly in constantly repeated prayer!
Source: The Treatises of Cyprian (New Advent)