It is reported that a group of heretics (People of Bid’ah) and their devout worship was mentioned to ‘Abd Al-Rahmân b. Mahdî. He said, “Allâh only accepts what conforms to what has been commanded and what is in the Sunnah.” Then he recited, And a monasticism which they (Christians) innovated, We did not ordain it upon them [Al-Hadîd: 27]. He went on to say, “So Allâh did not accept this from them and reprimanded them for it.” He then said, “Stick to the way and the Sunnah.”

Abû Nu’aym, Hilyah Al-Awliyâ` Vol.4 p44.