Einhard. The Life of the Emperor Charles. Chapter 4.
It would be folly, I think, to write a word concerning Charles' birth and infancy, or even his boyhood, for nothing has ever been written on the subject, and there is no one alive now who can give information of it. Accordingly, I have determined to pass that by as unknown, and to proceed at once to treat of his character, his deeds, and such other facts of his life as are worth telling and setting forth, and shall first give an account of his deeds at home and abroad, then of his character pursuits, and lastly of his administraton and death, omitting nothing worth knowing or necessary to know.
Text source: The Life of Charlemagne by Einhard. Translated by Samuel Epes Turner.