Doctrine of Addai

The Doctrine of Addai is a Syriac Christian text, perhaps written about 400, which recites the Legend of the Image of Edessa as well as the legendary works of Addai and his disciple Mari in Mesopotamia.

The story of how King Abgar and Jesus had corresponded was first recounted in the 4th century by the church historian Eusebius of Caesarea in his Ecclesiastical History (i.13 and iii.1) and it was retold in elaborated form by Ephrem the Syrian.

...
Wikipedia