The Didache is dated by most scholars to the end of the first century. It’s opening line (essentially its title) is: “Teaching of the Lord to the Gentiles (or Nations) by the Twelve Apostles”. It contains elements regarding Christian life and community, quoting and echoing the teachings of Jesus and the apostles.
“There are two ways, one of life and one of death, and there is a great difference between the two ways. The way of life is this. First of all, thou shalt love the God that made thee; secondly, Thy neighbor as thyself. And all things whatsoever thou wouldst not have befall thyself, neither do thou unto another. Now of these words the doctrine is this. Bless them that curse you, and pray for your enemies and fast for them that persecute you; for what thank is it, if ye love them that love you? Do not even the Gentiles the same? But do ye love them that hate you that hate you, and ye shall not have an enemy.” (Didache 1.1–3 AFL-E)