Chapter 33 — Part IV: Prayer — On Prayer in General
Section 71. Freedom From Violence, Anger, Hatred And Inhumanity — There are some crimes, such as violence and murder, which are in a special way obstacles to the efficacy of our prayers, and we must, therefore, preserve our hands unstained by outrage and cruelty. Of such crimes the Lord says by the mouth of Isaias: When you stretch forth your hands, I will turn away my eyes from you; and when you multiply prayer, I will not hear, for your hands are full of blood