Is Sufism haram or forbidden in Islam?

Authentic Tasawwuf is not forbidden: it is the science of ikhlas, or sincerity, needed by every Muslim, and of the states of the heart that the Shariah itself commands. What is forbidden is any false “Sufism” that sets itself against the Shariah.

The worry comes from seeing fake Sufis who claim that a pure heart excuses them from the law.

Mawlana Ashraf Ali Thanvi rahimahullah, answering the misconception that there is no need to adhere to the Shariah in Tasawwuf, cites al-Futuhat al-Makkiyya: “Tasawwuf that is against the Shariáh is irreligious and rejected. Whoever says that there is a path to Allah different to what the Shariáh has outlined, then he is a liar. Hence, a person who has no adab (prescribed Islamic etiquette) cannot be a Shaykh. We have no path to Allah except that which has come by way of Shariáh, and we have no path to Allah except that which the Shariáh has shown.” [Thanvi, Ta'lim al-Deen] That kind is indeed to be avoided.

But real Tasawwuf is the opposite. It is excellence (ihsan) in following the Qur'an and the Sunnah, aimed at the very states of the heart the Shariah orders: sincerity, fear of Allah, and love of the Prophet ﷺ. Far from being forbidden, it is what gives the outward acts of worship their soul.