All praise is due to Allah, and peace and blessings be upon our Master, the Messenger of Allah.
There is no harm in calling "Nazarenes" by the name "Christians," even though this term is not mentioned in the Quran. It is not a requirement for the naming of sects and religions to be explicitly stated in the Quran and Sunnah; it suffices that the name is commonly recognized and known among scholars without carrying any prohibitions of Sharia. The Quran may limit itself to certain names but does not negate the validity of others.
In the past as well as the present, Muslim scholars, have used the term "Christian" to refer to those who belong to the Nazarene faith. We find this in historical and biographical texts, such as "Uyoon al-Anbaa." The scholar al-Subki also mentioned this name in "Tabqat al-Shafi'iyyah " in verses attributed to Imam al-Qaffal al-Shashi, a Shafi'i scholar, may Allah have mercy on him.
We say this while affirming our belief that the Messiah, Jesus son of Mary, peace be upon them both, was a servant of Allah. Allah the Exalted said, conveying the words of Jesus, peace be upon him: “He said, 'Indeed, I am the servant of Allah. He has given me the Scripture and made me a prophet. And He has made me blessed wherever I may be and has enjoined upon me prayer and Zakat as long as I remain alive.'” [Maryam, 30-31]. And Allah The Almighty knows best.