Indulgences

• Tad R. Callister, "The Inevitable Apostasy", pp. 271-273

Discusses the sale of indulgences during the Great Apostasy as it relates to the overall wickedness of the clergy.

• William Langland, "The Vision of Piers Plowman", pp. 3-4, lines 68-82

14th century poem.
Cites the wickedness of the clergy in conspiring to sell indulgences. (and in other practices)

(Available in more modern English though without line numbers at http://www.historyguide.org/ancient/langland.html)