Justin Martyr — The First Apology of Justin — Written in 148 A.D. To 155 A.D.
Chapter LXVI. — Of the Eucharist.

And this food is called among us Eucharisti'a (5) [the Eucharist], of which no one is allowed to partake but the man who believes that the things which we teach are true, and who has been washed with the washing that is for the remission of sins, and unto regeneration, and who is so living as Christ has enjoined. For not as common bread and common drink do we receive these; but in like manner as Jesus Christ our Saviour, having been made flesh by the Word of God, had both flesh and blood for our salvation, so likewise have we been taught that the food which is blessed by the prayer of His word, and from which our blood and flesh by transmutation are nourished, is the flesh and blood of that Jesus who was made flesh. (6)

For the Apostles, in the memoirs composed by them, which are called Gospels, have thus delivered unto us what was enjoined upon them; that Jesus took bread, and when He had given thanks, said, "This do ye in remembrance of Me, (7) this is My body;" and that, after the same manner, having taken the cup and given thanks, He said, "This is My blood;" and gave it to them alone. Which the wicked devils have imitated in the mysteries of Mithras, commanding the same thing to be done. For, that bread and a cup of water are placed with certain incantations in the mystic rites of one who is being initiated, you either know or can learn.

Justin Martyr Dialogue with Trypho written in 155 A.D.
Chapter XLI. — The Oblation Of Fine Flour Was A Figure Of The Eucharist.

"And the offering of fine flour, sirs," I said, "which was prescribed to be presented on behalf of those purified from leprosy, was a type of the bread of the Eucharist, the celebration of which our Lord Jesus Christ prescribed, in remembrance of the suffering which He endured on behalf of those who are purified in soul from all iniquity, in order that we may at the same time thank God for having created the world, with all things therein, for the sake of man, and for delivering us from the evil in which we were, and for utterly overthrowing (4) principalities and powers by Him who suffered according to His will. Hence God speaks by the mouth of Malachi, one of the twelve [prophets], as I said before, (5) about the sacrifices at that time presented by you: 'I have no pleasure in you, saith the Lord; and I will not accept your sacrifices at your hands: for, from the rising of the sun unto the going down of the same, My name has been glorified among the Gentiles, and in every place incense is offered to My name, and a pure offering: for My name is great among the Gentiles, saith the Lord: but ye profane it.' (6) [So] He then speaks of those Gentiles, namely us, who in every place offer sacrifices to Him, i.e., the bread of the Eucharist, and also the cup of the Eucharist, affirming both that we glorify His name, and that you profane [it]. The command of circumcision, again, bidding [them] always circumcise the children on the eighth day, was a type of the true circumcision, by which we are circumcised from deceit and iniquity through Him who rose from the dead on the first day after the Sabbath, [namely through] our Lord Jesus Christ. For the first day after the Sabbath, remaining the first (7) of all the days, is called, however, the eighth, according to the number of all the days of the cycle, and [yet] remains the first.

Justin Martyr — The First Apology of Justin — Written in 148 A.D. to 155 A.D.
Chapter LXVII. — Weekly Worship of the Christians.

And we afterwards continually remind each other of these things. And the wealthy among us help the needy; and we always keep together; and for all things wherewith we are supplied, we bless the Maker of all through His Son Jesus Christ, and through the Holy Ghost. And on the day called Sunday, (1) all who live in cities or in the country gather together to one place, and the memoirs of the Apostles or the writings of the prophets are read, as long as time permits; then, when the reader has ceased, the president verbally instructs, and exhorts to the imitation of these good things. Then we all rise together and pray, and, as we before said, when our prayer is ended, bread and wine and water are brought, and the president in like manner offers prayers and thanksgivings, according to his ability, (2) and the people assent, saying Amen; and there is a distribution to each, and a participation of that over which thanks have been given, (3) and to those who are absent a portion is sent by the deacons. And they who are well to do, and willing, give what each thinks fit; and what is collected is deposited with the president, who succors the orphans and widows and those who, through sickness or any other cause, are in want, and those who are in bonds and the strangers sojourning among us, and in a word takes care of all who are in need. But Sunday is the day on which we all hold our common assembly, because it is the first day on which God, having wrought a change in the darkness and matter, made the world; and Jesus Christ our Saviour on the same day rose from the dead. For He was crucified on the day before that of Saturn (Saturday); and on the day after that of Saturn, which is the day of the Sun, having appeared to His Apostles and disciples, He taught them these things, which we have submitted to you also for your consideration.