Calling Christian Jew or calling Hindu Christian is not Kufr
21-12-2016 | IslamWeb
Question:
Assalaamu alaykum. If I were to call a Christian a Jew or a Hindu a Christian; would that constitute Kufr (disbelief) on my part given that they have different Kufr beliefs? Or would it not be Kufr to name one type of non-Muslim with a different type of non-Muslim appellation. My question is very urgent, please. May Allaah reward you.
Answer:
All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad 
is His slave and Messenger.
A person who says to a Christian, “O Jew,” or, “O Christian,” to a Hindu, for instance, is not accused of Kufr. Rather, even if someone says to a Muslim, “O disbeliever,” or, “O Christian,” he does not become a non-Muslim.
The warning against addressing a Muslim by saying, “O non-Muslim,” to him came in the hadeeth that was narrated by Ibn ‘Umar, may Allah be pleased with him, with the wording, “If a man says to his brother (i.e. his fellow Muslim): 'O disbeliever,' then it returns to one of them.” [Al-Bukhari and Muslim]
Another narration by Muslim reads, “If a man says to his brother (i.e. his fellow Muslim), 'O disbeliever,' and he is not so, then it returns back to him.”
Another narration by Muslim also reads, “If a man considers his Muslim brother as a disbeliever, then it falls back on one of them.”
The scholars interpreted this hadeeth to mean minor disbelief (Kufr Asghar) [and not major disbelief that takes a person out of the fold of Islam]. They provided the hadeeth narrated by Thaabit ibn adh-Dhahhaak, who said, “The Prophet said, ‘Cursing a Muslim is like killing him, and whoever accuses a believer of Kufr, it is like killing him.’” [Al-Bukhari] as evidence.
Killing is not Kufr, and declaring a Muslim as a disbeliever is likened to killing in the hadeeth. Shaykh Ibn Taymiyyah 
said in Al-Istiqaamah, “The Prophet called him a brother, and he said, ‘It falls back on him.’ If one of them had completely left Islam by saying that, then he would not be called his brother.”
Ibn Qudaamah said, “It is understood that the goal of these ahaadeeth is to emphasize the matter and liken (a Muslim) to non-Muslims, it does not mean that the person truly is a disbeliever. This is the meaning of the hadeeth and what is meant by ‘Kufr’ in it.”
For more benefit, please refer to fatwas 323092, 87963.
Allah knows best.