2 But many ask for what they ought not to ask, not knowing what is expedient for them. Two things therefore must he that prays beware of; that he ask not what he ought not; and that he ask not from whom he ought not. From the devil, from idols, from evil spirits, must nothing be asked. From the Lord our God Jesus Christ, God the Father of Prophets, and Apostles, and Martyrs, from the Father of our Lord Jesus Christ, from God who made heaven and earth, the sea, and all things in them, from Him must we ask whatsoever we have to ask. But we must beware that we ask not of Him that which we ought not to ask. If because we ought to ask for life, you ask it of dumb and deaf idols, what does it profit you? So if from God the Father, who is in heaven, you wish for the death of your enemies, what does it profit you? Have you not heard or read in the Psalm, in which the damnable end of the traitor Judas is foretold, how the prophecy spoke of him, “Let his prayer be turned into sin?” If then you rise up, and prayest for evil on your enemies, your “prayer will be turned into sin.”
Source: Sermons on Selected Lessons of the New Testament (New Advent)