Cyril of Jerusalem: Limit Theology to What is Written in Scripture

Cyril of Jerusalem (318-386): Let us assert of the Holy Spirit, therefore, only what is written; let us not busy ourselves about what is not written. The Holy Spirit has authored the Scriptures; He has spoken of Himself all that He wished, or all that we could grasp; let us confine ourselves to what He has said, for it is reckless to do otherwise.

Fathers of the Church, Leo P. McCauley, Vol. 64, The Works of Saint Cyril of Jerusalem, Catechesis Lecture 16, §2 (New York: Fathers of the Church, Inc., 1949), pp. 76-77.