Copied from the web: The English theologian and historian Thomas Fuller appears to be the first person to commit the notion that 'the darkest hour is just before the dawn' to print. The source of that proverb isn't known. It may be Fuller himself, or he may have been recording a piece of folk wisdom. In 1858, much later than Fuller of course, Samuel Lover attributed the notion to the Irish, in Songs and Ballads:
There is a beautiful saying amongst the Irish peasantry to inspire hope under adverse circumstances: "Remember...They say, "that the darkest hour of all is the hour before day."