Reference: Fataawa al-Lajnah ad-Daa.imah lil-Buhooth al-‘Ilmiyyah wal-Iftaa., – Volume 2, Page 301, Question 9 of Fatwa No.6250
Question: In the area where I live there is a masjid where there is a group who follow the way of the Sufis. Is it permissible to pray in this masjid?
Response: You should not pray with the Sufis in their masjid, and you must beware of their companionship and mixing with them in case you are afflicted with what they have been afflicted with. So perform your prayers in a[nother] msajid where they uphold the Sunnah and are steadfast upon it.
And with Allaah lies all success and may Allaah send prayers and salutations upon our Prophet (sal-Allaahu ‘alayhi wa sallam) and his family and his companions.