The Letter to the Smyrnaeans (often simply called To the Smyrnaeans) was written by Saint Ignatius of Antioch around AD 110 to the Early Christians in Smyrna.
It mentions the resurrection of Jesus: (2:1a) "Now, he suffered all these things for our sake, that we might be saved. And he truly suffered, even as he truly raised himself up; not as certain unbelievers say, that he suffered in semblance, they themselves only existing in semblance." The term translated "semblance" is the Greek work "dokeiv" from which the heresy of docetism got its name. The primary purpose of the letter to the Smyrnaeans is to counter those who make the claims of docetism.
To counter the teaching of the docetists, who claimed that Jesus did not come in the flesh, Ignatius wrote the first 7 sections demonstrating the real incarnation of Jesus, thus saying about the Eucharist (7:1) "They [the docetists] abstain from the Eucharist and from prayer, because they confess not the Eucharist to be the flesh of our Saviour Jesus Christ, which suffered for our sins, and which the Father, of His goodness, raised up again. They who deny the gift of God are perishing in their disputes".
The letter is also the earliest recorded evidence of the use of the term "catholic church."