Work as if everything depended on you; pray as if everything depended on God.
Attr. to St. Augustine. Also to St. Ignatius of Loyola. And to Martin Luther.
A generic Google turned up the usual fluff, but it also found the quotation attributed to St. Ignatius in CCC 2834, footnoted as “Attributed to St. Ignatius Loyola, cf. Joseph de Guibert, SJ, The Jesuits: Their Spiritual Doctrine and Practice, (Chicago: Loyola University Press, 1964), 148, n. 55.” That’s scarcely a primary source. But I got to wondering what the Latin text of the CCC gives as a citation, and it gives a better one: “Dictum sancto Ignatio de Loyola attributum; cf Petrus de Ribadeneyra, Tractatus de modo gubernandi sancti Ignatii, c. 6, 14: MHSI 85, 631.” [Saying attributed to St. Ignatius of Loyola; cf. Peter of Ribadeneira, Tract on the method of governing of Saint Ignatius.]
Peter of Rebadeneira was one of the early Jesuits, well-acquainted with St. Ignatius, and the first person to write a biography of him. I can’t locate an online copy of the work in question, but I’m willing to call this one for St. Ignatius pending further information.