I agree with the D.M. Canright article. It proves that the common claim against Sunday is erroneous.
The Epistle of Barnabas was read in all the churches and one of the reasons why the early church worshiped on the 1st day of the week (or the eighth day of creation).
Barnabas 15:1
Moreover concerning the Sabbath likewise it is written in the Ten
Words, in which He spake to Moses face to face on Mount Sinai;
And
ye shall hallow the Sabbath of the Lord with pure hands and with a
pure heart.
Barnabas 15:2
And in another place He saith;
If my sons observe the Sabbath then
I will bestow My mercy upon them.
Barnabas 15:3
Of the Sabbath He speaketh in the beginning of the creation;
And
God made the works of His hands in six days, and He ended on the
seventh day, and rested on it, and He hallowed it.
Barnabas 15:4
Give heed, children, what this meaneth;
He ended in six days. He
meaneth this, that in six thousand years the Lord shall bring all
things to an end; for the day with Him signifyeth a thousand years;
and this He himself beareth me witness, saying;
Behold, the day of
the Lord shall be as a thousand years. Therefore, children, in six
days, that is in six thousand years, everything shall come to an end.
Barnabas 15:5
And He rested on the seventh day. this He meaneth; when His Son
shall come, and shall abolish the time of the Lawless One, and shall
judge the ungodly, and shall change the sun and the moon and the
stars, then shall he truly rest on the seventh day.
Barnabas 15:6
Yea and furthermore He saith;
Thou shalt hallow it with pure hands
and with a pure heart. If therefore a man is able now to hallow
the day which God hallowed, though he be pure in heart, we have gone
utterly astray.
Barnabas 15:7
But if after all then and not till then shall we truly rest and
hallow it, when we shall ourselves be able to do so after being
justified and receiving the promise, when iniquity is no more and all
things have been made new by the Lord, we shall be able to hallow it
then, because we ourselves shall have been hallowed first.
Barnabas 15:8
Finally He saith to them;
Your new moons and your Sabbaths I cannot
away with. Ye see what is His meaning ; it is not your present
Sabbaths that are acceptable [unto Me], but the Sabbath which I have
made, in the which, when I have set all things at rest, I will make
the beginning of the eighth day which is the beginning of another
world.
Barnabas 15:9
Wherefore also we keep the eighth day for rejoicing, in the which
also Jesus rose from the dead, and having been manifested ascended
into the heavens.