There's a semi-regular feature on OB called "Rationality quotes".  In Marketing rationality, I'm claiming that for conservative religious people, using rationality instrumentally is as epistemically dangerous as for us to use faith instrumentally.  People object.  So to supplement that, I'm giving you a list of anti-rationality quotes.  I originally compiled them to respond to a theologian who claimed that Christianity encouraged inquisitiveness; but I think they apply to reason as well.  Please note that these quotes are not from obscure authors; all of these quotes, with the possible exception of Sturgeon, are from authors who are considered by Christians (either Catholics or Protestants) to be more authoritative than anyone alive today.

Some of these examples come from “Curiosity, Forbidden Knowledge, and the Reformation of Natural Philosophy in Early Modern England”, Peter Harrison, Isis, Vol. 92, No. 2 (June 2001), pp. 265-290; and from The Uses of Curiosity in Early Modern France and Germany, Neil Kenny (2004).  2 quotes come from chpt. 5 of Hitchens, God is Not Great.  (His Aquinas quote, however, says exactly the opposite of what Aquinas actually said.)  Some of them I found myself.

Also see the Wikipedia page on the Syllabus of Errors that byrnema provided.

ADDED:  ICMMT.  I concede that the relation between rationalists using unreason, and Christians using reason, is not symmetric.  But it is analogical.

• And when the woman saw that the tree was good for food, and that it was pleasant to the eyes, and a tree to be desired to make one wise, she took of the fruit thereof, and did eat, and gave also unto her husband with her; and he did eat.  – Genesis 3:6 (KJV)
  

• There is a way which seems right to a man, but its end is the way of death.  – Proverbs 14:12; Proverbs 16:25 (NASB)
  

• “Where were you when I laid the foundation of the earth?  Tell Me, if you have understanding, Who set its measurements?  Since you know.  Or who stretched the line on it?”  Job 38:4-5 (NASB)

• I will destroy the wisdom of the wise; the intelligence of the intelligent I will frustrate.  – God, quoted in Isaiah 29:14, NIV
  

• Seek not out things that are too hard for thee, neither search the things that are above they strength… Be not curious in unnecessary matters.  – Ben Sira (a book of the Septuagint Bible, still in the Eastern Orthodox Bible), circa 200BC
  

• Where is the wise man?  Where is the scholar?  Where is the philosopher of this age?  Has not God made foolish the wisdom of the world?  For since in the wisdom of God the world through its wisdom did not know him, God was pleased through the foolishness of what was preached to save those who believe.  – St. Paul, 1 Corinthians 1:20-21 (NIV)
  

• See to it that no one takes you captive through hollow and deceptive philosophy, which depends on human tradition and the basic principles of this world rather than on Christ.  – St. Paul, Colossians 2:8 (NIV)
  

• Turn away from godless chatter and the opposing ideas of what is falsely called knowledge, which some have professed and in so doing have wandered from the faith.  – St. Paul, 1 Timothy 6:20-21 (NIV)

• For philosophy is the material of the world’s wisdom, the rash interpreter of the nature and dispensation of God.  Indeed heresies are themselves instigated by philosophy… What indeed has Athens to do with Jerusalem? What has the Academy to do with the Church?  What have heretics to do with Christians?  Our instruction comes from the porch of Solomon, who had himself taught that the Lord should be sought in simplicity of heart.  Away with all attempts to produce a Stoic, Platonic, and dialectic Christianity!  We want no curious disputation after possessing Christ Jesus, no inquisition after receiving the gospel!  When we believe, we desire no further belief.  For this is our first article of faith, that there is nothing which we ought to believe besides. – Tertullian, circa 200AD

• The most penetrating mind cannot attain to the knowledge of the least of the phenomena of the world…  Put then a limit to your thought, so that your curiousity in investigating the incomprehensible may not incur the reproaches of Job, and you be not asked by him, “Whereupon are the foundations thereof fastened?”  – St. Basil the Great, circa 370AD
  

• Besides this there is yet another form of temptation still more complex in its peril. For in addition to the fleshly appetite which strives for the gratification of all senses and pleasures--in which its slaves perish because they separate themselves from thee--there is also a certain vain and curious longing in the soul, rooted in the same bodily senses, which is cloaked under the name of knowledge and learning; not having pleasure in the flesh, but striving for new experiences through the flesh. This longing--since its origin is our appetite for learning, and since the sight is the chief of our senses in the acquisition of knowledge--is called in the divine language “the lust of the eyes.” … This malady of curiosity is the reason for all those strange sights exhibited in the theater. It is also the reason why we proceed to search out the secret powers of nature--those which have nothing to do with our destiny—which do not profit us to know about, and concerning which men desire to know only for the sake of knowing.  – St. Augustine, Confessions, 397AD
  

• Is it not evident that a man who day and night wrestles with the dialectic art, the student of natural science whose gaze pierces the heavens, walks in vanity of understanding and darkness of mind? – St. Jerome, circa 400AD
  

• Rightly is curiosity considered the first step of pride; it was the beginning of all sin. – St. Bernard of Clairvaux, 12^th century
  

• [Curiousity may be a sin in 4 ways:]  Thirdly, when a man desires to know the truth about creatures, without referring his knowledge to its due end, namely, the knowledge of God. Hence Augustine says (De Vera Relig. 29) that "in studying creatures, we must not be moved by empty and perishable curiosity; but we should ever mount towards immortal and abiding things.” – St. Thomas Aquinas, Summa Theologica 2.2.167, 1265-1274AD

• Dei sacrificium intellectus. (We sacrifice the intellect to God.) – St. Ignatius Loyola, "To the members of the society in Portugal", 1553

• Eve erred in not regulating the measure of her knowledge by the will of God. And we all daily suffer under the same disease, because we desire to know more than is right, and more than God allows; whereas the principal point of wisdom is a well-regulated sobriety in obedience to God. – John Calvin, Commentary on Genesis 3:5, 1554
  

• We say, pronounce, sentence, and declare that you, the said Galileo, by reason of the matters adduced in trial, and by you confessed as above, have rendered yourself in the judgment of this Holy Office vehemently suspected of heresy, namely, of having believed and held the doctrine—which is false and contrary to the sacred and divine Scriptures—that the Sun is the center of the world and does not move from east to west and that the Earth moves and is not the center of the world; and that an opinion may be held and defended as probable after it has been declared and defined to be contrary to the Holy Scripture; and that consequently you have incurred all the censures and penalties imposed and promulgated in the sacred canons and other constitutions, general and particular, against such delinquents.  –Papal condemnation of Galileo, 1633
  

• If God has concealed anything, it is God’s glory to conceal it, and it is right that it should be hidden. If God has not told us any truth, it is for his glory not to tell it to us.  – Charles Spurgeon, 1877AD