This text comes from a document known as the Didache. The Didache is an early Christian document that was likely written around the year 100 A.D. The passage quoted here is Didache 16:1-8.
Watch over your life. Don’t let your lamps go out nor let your loins be ungirded, but be prepared, for you do not know the hour in which our Lord will come. But gather often together, seeking the things which are gain for your souls, for the entire time of your faith will do you no good unless you are found complete at the last time; for in the last days the false prophets and the corruptors will become many, and sheep will turn into wolves, and love will change into hate; for as lawlessness grows, they will hate each another and persecute and betray.
Then the deceiver of the world shall appear like a son of God, and will work signs and wonders, and the earth shall be given over into his hands. He shall commit crimes the likes of which have never happened since the world began. Then, created humankind will come to fiery trial. Many will take offense and be lost, but those who keep in their faith shall be saved through the curse itself. And then shall appear the signs of the truth: First the sign spread out over the sky, then the sign of the trumpet sound, and thirdly the resurrection of the dead! But not of all the dead; as it was said, “The Lord will come, and all his saints with him.” Then the world will see the Lord coming on the clouds of heaven.