Quote from the Epistel of Barnabas (100AD or less)
Generally accepted to be the genuine Barnabas, Paul's companion.
Chap. XV.  The False and the True Sabbath.
Further,145 also, it is written concerning the Sabbath in the Decalogue which [the Lord] spoke, face to face, to Moses on Mount Sinai, “And sanctify ye the Sabbath of the Lord with clean hands and a pure heart.†(Exo_20:8; Deu_5:12) And He says in another place, “If my sons keep the Sabbath, then will I cause my mercy to rest upon them.†(Jer_17:24, Jer_17:25) The Sabbath is mentioned at the beginning of the creation [thus]: “And God made in six days the works of His hands, and made an end on the seventh day, and rested on it, and sanctified it.â€Â146 Attend, my children, to the meaning of this expression, “He finished in six days.†This implieth that the Lord will finish all things in six thousand years, for a day is147 with Him a thousand years. And He Himself testifieth,148 saying, “Behold, to-day149 will be as a thousand years.†(Psa_90:4; 2Pe_3:8) Therefore, my children, in six days, that is, in six thousand years, all things will be finished. “And He rested on the seventh day.†This meaneth: when His Son, coming [again], shall destroy the time of the wicked man,150 and judge the ungodly, and change the sun, and the moon,151 and the stars, then shall He truly rest on the seventh day. Moreover, He says, “Thou shalt sanctify it with pure hands and a pure heart.†If, therefore, any one can now sanctify the day which God hath sanctified, except he is pure in heart in all things,152 we are deceived.153 Behold, therefore:154 certainly then one properly resting sanctifies it, when we ourselves, having received the promise, wickedness no longer existing, and all things having been made new by the Lord, shall be able to work righteousness.155 Then we shall be able to sanctify it, having been first sanctified ourselves.156 Further, He says to them, “Your new moons and your Sabbath I cannot endure.†(Isa_1:13) Ye perceive how He speaks: Your present Sabbaths are not acceptable to Me, but that is which I have made, [namely this,] when, giving rest to all things, I shall make a beginning of the eighth day, that is, a beginning of another world. Wherefore, also, we keep the eighth day with joyfulness, the day also on which Jesus rose again from the dead.157 And158 when He had manifested Himself, He ascended into the heavens.