Imaam Al-Barbahaaree (rahimahullaah) said:
“Beware of the smaller newly introduced affairs, for indeed the smaller innovations develop until they become great. Such was the case with every innovation which was introduced into this Ummah; its origin was small – resembling the truth, so due to that those who entered into it were beguiled by it – and then could not exit from it. Thus it expanded and became a part of the religion – professed as religiousness.
So observe – may Allaah have mercy upon you, the speech of everyone you hear; particularly from the people of your time, do not be hasty and do not enter into anything from it until you ask and observe: did anyone from the companions of the Messenger (Sallallaahu ‘alaihi wa sallam) speak regarding this? – Or one of the Scholars?
For if you acquire a narration from them (regarding it) then hold onto it and do not go beyond it for anything and do not choose anything over it – and thus you should fall into The Fire.
Know may Allaah have mercy upon you, that the Islaam of a servant is not complete until he follows, attests and has submission (to it). So whoever claims that there is something remaining from the affair of Islaam which the companions of the Messenger (Sallallaahu ‘alaihi wa sallam) did not suffice us with then he has belied them; and sufficient is this as division and as a means of speaking ill of them. So he is an innovator, astray and leads others astray, one who introduces into Islaam that which is not from it.”
(Taken from: Hajjatun Nabi (Sallallaahu ‘alaihi wa sallam) [by Shaikh Al-Albaanee] p.103-104)
 Shaikh Al-Albaanee (rahimahullaah) said on p.103: “He was the great Imaam, from the scholars of the earlier Muslims: Shaikh Hasan bin ‘Alee Al-Barbahaaree, from the companions of the companions of Imaam Ahmad (rahimahullaah) who died in the year 329H.”
Note: for the complete treatise by Imaam Al-Barbahaaree from which the above extract is taken refer to the book: ‘Sharhus Sunnah’ (Explanation of The Creed).