This is the famous passage from St. Augustine’s Confessions (Lib 1,1-2,2.5,5: CSEL 33, 1-5) in which Saint Augustine states
“You have made us for yourself, O Lord, and our heart is restless until it rests in you.”
It is used in the Roman Office of readings for the Ninth Sunday in Ordinary time with the accompanying biblical reading of Job 28:1-28.