How far, O rich, do you extend your senseless avarice? Do you intend to be the sole inhabitants of the earth? Why do you drive out the fellow sharers of nature, and claim it all for yourselves? The earth was made for all, rich and poor, in common. Why do you rich claim it as your exclusive right? The soil was given to the rich and poor in common — wherefore, oh, ye rich, do you unjustly claim it for yourselves alone? Nature gave all things in common for the use of all; usurpation created private rights. Property hath no rights. The earth is the Lord’s, and we are his offspring. The pagans hold earth as property. They do blaspheme God.

Ambrose of Milan (339-397) Roman theologian, statesman, Christian prelate, saint, Doctor of the Church [Aurelius Ambrosius]

(Attributed)

Frequently quoted in the early 20th Century in various social justice writings, and in the years since then, but all citations I can find fall back to its inclusion in Upton Sinclair, The Cry for Justice, Book 8 "The Church" (1915) (though it can be found somewhat earlier than that).