Shaikh Rabee' bin Hadee al-Madkhalee (hafidhahullaah) stated:
When you see a person speaking ill of Ahlis-Sunnah, then this is an indication that this person is a deviant. It's also possible that he's a Zindeeq (heretic). When you see a person speaking ill of Ahlis-Sunnah and Ahlil-Hadeeth, what is it that causes him to speak ill of them except that he is in opposition to them and looking down upon that which is with them. There's no doubt in that.
If this is not the case, then what pushes him to speak ill of Ahlis-Sunnah and its followers?! Nothing pushes him except that he is one who is misguided, embodying deviance, vice and evil. This is from their (i.e. the people of Bid'ah's) signs. This is from the signs of the people of evil and the people of innovation. If he was to say: "I from Ahlis-Sunnah" don't believe him because he is a Kadh-dhaab (habitual liar)! Many from these fraudulent liars say to you: "I'm Salafi" and at the same time he's a liar. He only said this as a means of a plot (against the people of the Sunnah).
Similar to the Munaafiq (hypocrite) who says: "I'm a believer", "I'm a Muslim". He's says "I'm a Muslim"! The Munaafiq doesn't say: "I'm a Kaafir", or "I'm a Munaafiq and I hate Islaam." Rather he says "I'm a Muslim," he prays, give charity, and he does and does...at the same time he combats Islaam and hates the people of Islaam.
Many from amongst the people nowadays who say: "I'm Salafi," however you don't see him except that he hates the people of Hadeeth and speaks ill of them.
Source: Taken from Shaikh Rabee's Explanation of Aqeedatus-Salaf Ashaabil-Hadeeth, pg. 309
Translated by: Abu Yusuf Khaleefah