Calling others Kafirs? Shows your background.
Dilon k Haal Allah Behtar janta hai
Abu Zarr reported that the Holy Prophet said: No man accuses another man of being a sinner, or of being a kafir, but it reflects back on him if the other is not as he called him.'' (Bukhari, Book of Ethics; Book 78, ch. 44)
"Whoever attributes kufr [unbelief] to a believer, he is like his murderer.'' (Tirmizi, ch. Iman (Faith); see Arabic-Urdu edition cited earlier, vol. ii, p. 213. See also Bukhari, Book of Ethics; Book 78, ch. 44)