Library Eusebius of Caesarea Life of Constantine
Book 4
Chapter 17: Of his Prayers in the Palace, and his Reading the Holy Scriptures
Still nobler proofs of his piety might be discerned by those who marked how he modeled as it were his very palace into a church of God, and himself afforded a pattern of zeal to those assembled therein: how he took the sacred scriptures into his hands, and devoted himself to the study of those divinely inspired oracles; after which he would offer up regular prayers with all the members of his imperial court.
English translation by Ernest Cushing Richardson, in Nicene and Post-Nicene Fathers, Series II, Vol. I (eds. Philip Schaff and Henry Wace; Buffalo: Christian Literature Publishing Co., 1890). Public domain. Digital text via New Advent Church Fathers.