Al-‘Allaamah Al-Faqeeh the Noble Scholar Muhammad ibn Saaleh Al-Uthaymeen (rahimahullah) was asked regarding the books of the Soofiyah, 

He responded, my view with regards to tassawuf is the same as to other than it from that which has been innovated into al-Islaam. The Messenger of Allah clarified this when he said,

“Upon you is my sunnah, and the sunnah of the rightly guided caliphs after me; and be warned of newly innovated matters, for every innovation is misguidance.” (1)

Therefore, tasawwuf (and it’s people) are in opposition to the guidance of the Messenger (peace and blessings upon him), innovation and misguidance is obligatory for the Muslim to stay far away from. He should take his path to Allah from the Book of Allah and the Sunnah of His Messenger. 

As for the books of tasawwuf, then it is impermissible to acquire them or review (or read) them, except(2) for an individual (who is qualified to do so; i.e. a person of knowledge) who wants to know what is in them of innovation, so as to refute it; (in this instance) this persons looking through them is of a tremendous benefit. 

And this benefit is: refuting this innovation so that the people are safe from it. And this is an affair which is sought after; if the person is safe from deviating by way of these books.

Fataawa Nur ala ad-Darb Vol.2 Pg.66 Fatwa 675 

(1) Ahmad, Abu Dawood, At-Tirmidhi and Ibn Maajah

(2) See following links for more details regarding books of innovators and their harms

https://salaficentre.com/2013/04/reading-the-books-of-the-innovators-ash-shaykh-saalih-al-fawzaan/

Shaykh Rabee (hafidahullah) clarifies two dangerous doubts; one of them regarding books of people of misguidance; he explains the harms and gives examples of knowledgeable individuals, scholars, who fell into misguidance due to doubts of the people of misguidance. 

https://salaficentre.com/2017/02/24652/