Thaddeei Evangelium mentioned in the Decret. Gelasii de Libris Apocryphis (in Jus Canonicum, 15:3). Unless there is an erroneous reading for Matthew, it would either belong to the apostle Judas Thaddaeus or to a Judas belonging to the seventy whom Thomas sent to Edessa to king Abgar (Eusebius, Hist. Eccles. 1, 13; see Fabricius, Codex Apocryphus, 1, 136, 379). But tradition does not determine whether Thaddaeus who was sent to Abgar belonged to the twelve or the seventy, on which point Eusebius and Jerome disagree. See Eusebius, Hist. Eccles. (ed. Reading), p. 38, note 5, 6.
On the correspondence between Abgar and Jesus, see especially Hofmann, Leben Jesu nach den Apokryphen (Leips. 1851), p. 307 sq, (B. P.)