Imaam Hanbal says: “Nifaaq is disbelief…”
“It is important to understand that the munafiquun are the kufaar. It is important to understand this because you find too often individuals who will accuse others of being hypocrites, and say things like, “You are a munaafiq, etc.” This is a tremendously dangerous statement to say because saying such a thing is saying your brother is a kaafir. This is one. (Secondly), a person saying such a thing is as if he is claiming that he has knowledge of the unseen. This is because in order to say a person is a munaafiq, you have to know what is in his heart. You have to know that he is acting like a Muslim, but really doesn’t believe in Islaam. None of us has the ability to know these things. None of us. . .
So it is incumbent that we do not say the likes of these expressions. We (should not) go around calling our brothers and sisters hypocrites. We do not go around calling them hypocrites. But, what is more correct is if we find from them a characteristic that agrees with the characteristics of the hypocrites, like those whom the Prophet (salallaahu ‘alayhe wasallam) mentioned – for example, when they give a promise, they break it. So if we find from our brothers or sisters characteristics from the characteristics of the hypocrites like (the aforementioned), for example, then we can say: “Fear Allaah. You are acting like a hypocrite” or “You are doing like what the hypocrites do. Fear Allaah.” But (as for) calling them a hypocrite, then no – stay away from this. This is because nifaaq is kufr (disbelief).”
 Nifaaq, by Ustaadh Abu Abdis-Salaam Al-Juyaanee
 Transcribed by Umm Sufyaan Fatimah