Bruce M. Metzger and Bart D. Ehrman, "The Text of the New Testament: Its Transmission, Corruption and Restoration", Oxford University Press (New York – Oxford 2005), p. 79.
C. R. Gregory, "Textkritik des Neuen Testamentes", J.C. Hinrichs’sche Buchhandlung: Leipzig 1900, vol. 1, p. 103.