The Lord Jesus teaches us in Luke 6:31-36
Do to others as you would have them do to you. “If you love those who love you, what credit is that to you? For even sinners love those who love them. If you do good to those who do good to you, what credit is that to you? For even sinners do the same. If you lend to those from whom you hope to receive, what credit is that to you? Even sinners lend to sinners, to receive as much again. But love your enemies, do good, and lend, expecting nothing in return. Your reward will be great, and you will be children of the Most High; for he is kind to the ungrateful and the wicked. Be merciful, just as your Father is merciful.
About the year 100AD, a Christian document, The Didache, brought forth the Gospel teaching to the next generation of Christians:
“There are two ways; the one is that of life and the other is that of death. There is a great difference between the two ways. The Way of Life is this: first, you shall love the God Who made you; second, you shall love your neighbor as yourself. Everything that you do not wish to be done to you, do not do to another! Bless those who curse you, and pray for your enemies. Fast for those who persecute you, for what grace would you receive if you love only those who love you back? Even the heathen do that. Love those who hate you, and you will have no enemies. If someone strikes you on the right cheek, turn the other to him also, and you will be perfect.” ( What the Church Fathers Say About….Volume 2, pp. 137-138)