I am looking for the first extant record of Sunday being referred to specifically as the "Sabbath" or "Christian Sabbath"
I am not asking which day the early church gathered.
I am not asking which day is the Christian Sabbath.
I am not looking for evidence of the transfer of observance or meaning of the Sabbath from Saturday to Sunday, but for evidence of the transfer of title or label of "Sabbath" to Sunday.
I am asking for the first record of Sunday being labeled the Christian equivalent of the Jewish Sabbath.
Context of my question:
It is quite evident to me that in many early church writings that the idea of the Jewish Sabbath is actually rejected. Sunday was certainly a common day of gathering and to the Jewish believers the seventh day would still have possibly been thought of as the Sabbath day. But from Justin Martyr through the Council of Laodicea a Judaizing celebration of any Sabbath is discouraged and the true Sabbath is not any singular day, but as a status in Christ and an attitude of repentance and rest in Him.
I understand many may even disagree with the above statements, but I tell you this so you can understand what kind of statement I am looking for and the question can be answered regardless. At some point in Christian theology someone labeled Sunday not just a day to gather or even a day to rest and enjoy a Sabbath, but someone labeled it as the Christian Sabbath. A true shift of the same Sabbath from the Jewish seventh day to a Christian first day.
Also many may agree with me, even to the point that the idea of Sunday Sabbath seems foreign or wrong. This question remains agnostic on which is right and on what the source may have truly meant.
Finding the earliest record would certainly impact answers to related questions, but all that is outside the bounds of this question.
When is Sunday first recorded as being labeled the Sabbath? Not just a day of rest or gathering or worship.
From About Christianity website:
Today, many Christian traditions believe Sunday is the Christian Sabbath day.
Westminster Confession Chapter 21 Article 7:
He has particularly appointed one day in seven, for a Sabbath, to be kept holy unto him: which, from the beginning of the world to the resurrection of Christ, was the last day of the week: and, from the resurrection of Christ, was changed into the first day of the week, which, in Scripture, is called the Lord's Day, and is to be continued to the end of the world, as the Christian Sabbath.
A lengthily titled treatise on the Sabbath by John Owen says:
And for a holy day of rest, ...he determined the observation of the first day of the week; ... Now, as God’s rest, and his being refreshed in his work, on the seventh day of old, ... so the rest of our Lord Jesus Christ, and his being refreshed in and from his works, on the first day, is a sufficient indication of the precise day of rest to be observed under the dispensation of the new covenant, now confirmed and established (pp. 409-410).
I'm not entirely sure that is how Owen meant it but that is how that part alone could be understood (the treatise is quite long, the above link is a summary with quotations). So perhaps this is a "missing link" of sorts in the direction of the earlier quotes.