Just to provide a bit more information on what Buzuxi02 said, circumcision is written about negatively in certain parts of the History of the Patriarchs of Alexandria (a collection of previous and contemporary biographies and histories, begun in the 10th century by Bp. Severus El Ashmunein), showing that it was known in that time, but still enough of a novelty/innovation to be recognized as unacceptable and foreign. From that source, the earliest evidence we have for the Coptic practice of circumcision is from the biography of John, bishop to the Abyssinians during the time of HH Abba James (50th Coptic Patriarch, 819-830), but it came about in an odd way that didn't really have anything to do with Muslims or Islam (that influence came even later). On the strength of the witness of John II, writing in 866 the biographies of patriarchs Mina I (767-744) to Shenouda I (whose papacy was contemporaneous with John II's writing, and would not end until 880), we are told that in the time of HH Pope James, he ordained one Abba John to be bishop to the Abyssinians. At that time, the Abyssinians were at war and were not welcoming to outsiders, and hence drove out the bishop and elected one of their own, in violation of the canons. So John returned to Egypt to the monastery of El Baramous in Wadi Habib, where he had previously been a monk.
After the Abyssinians subsequently lost their war and were beset by famine and drought, their king wrote to the patriarch, asking him to please send Bp. John back to them. The patriarch obliged. Here the biography shows its disdain for the practice of circumcision, in its phrasing concerning what happened next:
“After this, Satan, the enemy of peace, suggested an idea to some of the people of that country. Accordingly, they waited upon the king, and said to him: “We request thy majesty to command this bishop to be circumcised. For all the inhabitants of our country are circumcised except him”. And the working of Satan was so powerful that the king approved this proposal, namely that the aged bishop should be taken and circumcised, or else that he should return to the place whence he had come. And when the bishop recollected the hardships of his journeys, both when he departed and when he returned, and then of what he would experience again, he dreaded the difficulties of the road both by land and water. So he said: “I will submit to this, for the salvation of these souls, of which the Lord has appointed me shepherd without any merit of mine. Yet now Paul the apostle enjoins us, saying: ‘If any man is called without circumcision, let him not be circumcised’”.
From this we can learn two things: still in the 9th century, the circumcision of Christians was being called by the Copts an idea that came from Satan (!), and that the first Copt to submit to the practice did so in order to be accepted by the Ethiopians, not the Muslims. Even in accepting it, John himself does not allow for any confusion as to whether or not the practice ought to be commanded of Christians, with his quote from St. Paul.
We can tell by looking at subsequent canons that Islamic influence in Egypt had grown within about two and a half centuries of HH James' time such that probably no bishop could've stopped it by that point, but I just thought it was interesting to see the very beginning of Coptic circumcision, because before I got my own copy of the History of the Patriarchs, I had thought it was as simple as Muslim influence, too. (This being repeated in several sources, including later Coptic sources, which are not wrong about why it has unfortunately remained a part of many people's practice despite the canons against it.)