Ye have heard that it hath been said, An eye for an eye, and a tooth for a tooth: But I say unto you, That ye resist not evil: but whosoever shall smite thee on thy right cheek, turn to him the other also. And if any man will sue thee at the law, and take away thy coat, let him have thy cloak also. And whosoever shall compel thee to go a mile, go with him twain. Give to him that asks thee, and from him that would borrow of thee turn not thou away. Ye have heard that it hath been said, Thou shalt love thy neighbour, and hate thine enemy. But I say unto you, Love your enemies, bless them that curse you, do good to them that hate you, and pray for them which despitefully use you, and persecute you; that ye may be the children of your Father which is in heaven: for he maketh his sun to rise on the evil and on the good, and sends rain on the just and on the unjust. For if ye love them which love you, what reward have ye? do not even the publicans the same? And if ye salute your brethren only, what do ye more than others? do not even the publicans so? Be ye therefore perfect, even as your Father which is in heaven is perfect. Matthew 5:38-48
There are two ways, one of life and one of death, but a great difference between the two ways. The way of life, then, is this: First, you shall love God who made you; second, love your neighbor as yourself, and do not do to another what you would not want done to you. And of these sayings the teaching is this: Bless those who curse you, and pray for your enemies, and fast for those who persecute you. For what reward is there for loving those who love you? Do not the Gentiles do the same? But love those who hate you, and you shall not have an enemy. Abstain from fleshly and worldly lusts. If someone strikes your right cheek, turn to him the other also, and you shall be perfect. If someone impresses you for one mile, go with him two. If someone takes your cloak, give him also your coat. If someone takes from you what is yours, ask it not back, for indeed you are not able. Give to every one who asks you, and ask it not back; for the Father wills that to all should be given of our own blessings (free gifts). Didache (A.D. 80-140) ch.1
Against their outbursts of wrath be you meek; against their proud words be you humble; against their railings set you your prayers; against their errors be you steadfast in the faith; against their fierceness be you gentle. And be not zealous to imitate them by requital. Let us show ourselves their brothers by our forbearance; but let us be zealous to be imitators of the Lord, vying with each other who shall suffer the greater wrong, who shall be defrauded, who shall be set at naught; that no herb of the devil be found in you: but in all purity and temperance abide you in Christ Jesus, with your flesh and with your spirit. Ignatius: to the Ephesians (A.D. 35-105) ch.5
We who hated and destroyed one another, and on account of their different manners would not live with men of a different tribe, now, since the coming of Christ, live familiarly with them, and pray for our enemies, and endeavour to persuade those who hate us unjustly to live conformably to the good precepts of Christ, to the end that they may become partakers with us of the same joyful hope of a reward from God the ruler of all. Justin Martyr (A.D. 160) Ante-Nicene Fathers vol.1 pg.167
We who formerly used to murder one another do not only now refrain from making war upon our enemies, but also, that we may not lie nor deceive our examiners, willingly die confessing Christ.Justin Martyr (A.D. 160) Ante-Nicene Fathers vol.1 pg.176
And concerning our being patient of injuries, and ready to serve all, and free from anger, this is what He said: “To him that smites you on the one cheek, offer also the other; and him that takes away your cloak or coat, forbid not. And whosoever shall be angry, is in danger of the fire. And every one that compels you to go with him a mile, follow him two. And let your good works shine before men, that they, seeing them, may glorify your Father which is in heaven.” For we ought not to strive; neither has He desired us to be imitators of wicked men, but He has exhorted us to lead all men, by patience and gentleness, from shame and the love of evil. And this indeed is proved in the case of many who once were of your way of thinking, but have changed their violent and tyrannical disposition, being overcome either by the constancy which they have witnessed in their neighbors’ lives, or by the extraordinary forbearance they have observed in their fellow-travelers when defrauded, or by the honesty of those with whom they have transacted business. Justin Martyr (A.D. 160) Ante-Nicene Fathers vol.1 pg.168
But they who were brought up licentiously in wicked customs, and are prejudiced in their own opinions, should kill and hate us; whom we not only do not hate, but, as is proved, pity and endeavour to lead to repentance. Justin Martyr (A.D. 160) Ante-Nicene Fathers vol.1 pg.182
These we hold in contempt, though to the generality they appear matters of great importance; for we have learned, not only not to return blow for blow, nor to go to law with those who plunder and rob us, but to those who smite us on one side of the face to offer the other side also, and to those who take away our coat to give likewise our cloak. But, when we have surrendered our property, they plot against our very bodies and souls, pouring upon us wholesale charges of crimes of which we are guiltless even in thought, but which belong to these idle praters themselves, and to the whole tribe of those who are like them. Athenagorus (A.D. 137) Ante-Nicene Fathers vol.2 pg.129
If we are commanded, then, to love our enemies, as I have remarked above, whom have we to hate? If injured, we are forbidden to retaliate, lest we become as bad ourselves: who can suffer injury at our hands? Tertullian (A.D. 198) Ante-Nicene Fathers vol.3 pg. 45
For all love those who love them; it is peculiar to Christians alone to love those that hate them. Tertullian (A.D. 198) Ante-Nicene Fathers vol.3 pg. 105