Gordon D. Fee, "On the Inauthenticity of John 5:3b-4," The Evangelical Quarterly 54.4 (1982): 207-218.
John 5:3-4 reads in the King James Version: "In these lay a great multitude of impotent folk, of blind, halt, withered, waiting for the moving of the water. For an angel went down out at a certain season into the pool, and troubled the water: whoever then first after the troubling of the water stepped in was made whole of whatever disease he had."
Fee's article gives a rationale as to why this text was not part of the original autograph.
HT: Paul Bradshaw