Einhard. The Life of the Emperor Charles. Chapter 2.
At the time of Childreic's deposition, Pepin, the father of King Charles, held this office of Mayor of the Palace, one might almost say, by hereditary right; for Pepin's father, Charles, had received it at the hands of his father, Pepin, and filled it with distinction. It was this Charles that cursed the tyrants who claimed to rule the whole Frank land as their own, and that utterly routed the Saracens, when they attempted the conquest of Gaul in two great battles ‹ one in Aquitania, near the town of Poitiers, and the other on the River Berre, near Narbonne ‹ and compelled them to return to Spain. This honor was usually conferred by the people only upon men eminent from their illustrious birth and ample wealth. For some years, ostensibly under King Childeric, Pepin, the father of King Charles, shared the duties inherited from his father and grandfather most amicably with his brother, Carloman. The latter, then, for reasons unknown, renounced the heavy cares of an earthly crown and retired to Rome. Here he exchanged his worldly garb for a cowl, and built a monastery on Mt. Oreste, near the Church of St. Sylvester, where he enjoyed for several years the seclusion that he desired, in company with certain others who had the same object in view. But so many distinguished Franks made the pilgrimage to Rome to fulfill their vows, and insisted upon paying their respects to him, as their former lord, on the way, that the repose which he so much loved was broken by these frequent visits, and he was driven to change his abode. Accordingly, when he found that his plans were frustrated by his many visitors, he abandoned the mountain, and withdrew to the Monastery of St. Beneditct, on Monte Cassino, in the province of Samnium, and passed the rest of his days there in the exercises of religion.
Text source: The Life of Charlemagne by Einhard. Translated by Samuel Epes Turner.