Clement of Alexandria

We must therefore sleep so as to be easily awaked... For there is no use of a sleeping man, as there is not of a dead man. Wherefore we ought often to rise by night and bless God. For blessed are they who watch for Him, and so make themselves like the angels, whom we call "watchers." But a man asleep is worth nothing, any more than if he were not alive. But he who has the light watches, "and darkness seizes not on him," nor sleep, since darkness does not. He that is illuminated is therefore awake towards God; and such an one lives... "Let us not then sleep, as do others, but let us watch," says the Scripture, "and be sober. For they that sleep, sleep in the night; and they that be drunken, are drunken in the night," that is, in the darkness of ignorance. "But let us who are of the day be sober. For ye are all children of the light, and children of the day; we are not of the night, nor of the darkness."