"In the case of the soul, on the other hand, none of these things is necessary, unless, just as you daily spend money to give nourishment to the body, you are likewise determined not to neglect the soul and let it die of hunger but to provide it with proper nourishment from the reading of Scripture and the support of spiritual advice: “Not on bread alone does man live,” Scripture says, remember, 'but on every word coming from the mouth of God.' "
Source: FC, Vol. 82, Homilies on Genesis 18-45, Homily 21.22 (Washington, D.C.: The Catholic University of America Press, 1990), p. 66.
For an excellent compilation of quotes of the Church fathers teaching on the primacy, sufficiency and ultimate authority of Scripture, get a copy of Holy Scripture:The Ground and Pillar of Our Faith Vol III- The Writings of the Church Fathers Affirming the Reformation Principle of Sola Scriptura.