Many Western people consider Sufism as an eastern religion which has nothing to do with Islam. However, the majority of Sunni Muslims believe that Sufism cannot be separated from Islam. In fact, the idea that Sufism comes from eastern religions and is different from "pure" Islam comes from Wahhabis. Many Western researchers actually took this idea from them.
In this post, I am going to write about the place of Sufism in Sunni Islam. In another blog, I wrote that Islam has three main components:
1. Iman (faith)
2. Islam (this word here means rituals of worship)
3. Ihsan (sincerity)
Iman (faith) is the subject of Muslim theology (aqidah and kalam). Islam (rituals of worship) is the subject of Muslim law (fiqh). The word "ihsan" is usually translated as "sincerity." It corresponds with the third part of Islam which is ethics, moral and spiritual perfection. These things are subjects of Muslim ethics (ahlak) and tasawwuf. Tasawwuf is Arabic word for Sufism. Thus, Sufism's goal is moral and spiritual perfection. Muslim law (fiqh and shariah) deal with the outward behavior of Muslims. Sufism has to do with their inward spiritual condition, growth, and perfection. Thus, most Sunni Muslims consider Sufism as the heart of Islam.
Traditional Sufi groups require their members to be Muslims who follow shariah before they can follow Sufi tariqahs (the word "tariqah" literally means "way").
In Sunni Islam, there are four madhabs (schools) in fiqh: Hanafi, Shafii, Maliki, and Hanbali madhabs. There are also two madhabs in aqidah: Ashariyya (Ashari madhab) and Maturidiyya (Maturidi madhab). Most Sunnis follow Ashariyya, but Turkish-speaking Hanafis follow Maturidiyya. In Russia and other countries of the former Soviet Union, most Muslims are Maturidis and Hanafis with the exception of Chechens and most Daghestanis who are Asharis and Shafiis. In Sufism, there are many tariqahs, for example: Naqshbandi, Qadiri, Shadhili, and others.
Most Chechens follow Ashariyya in aqidah, Shafii madhab in fiqh, and Qadiri tariqah in tasawwuf. Most Avars (this is the biggest nation in Daghestan) follow Ashariyya in aqidah, Shafii madhab in fiqh, and Naqshbandi tariqah in tasawwuf.
Thus, Sufism is the part of Sunni Islam and there is no least contradiction between Sunni Islam and Sufism. A Sunni Islam is able to be a Sufi at the same time. Moreover, traditional Sunni Islam encourage people to become Sufis and some Sunnis even consider that it is mandatory for Muslims to be Sufis. However, it is obviously that a Muslim cannot be a Buddhist, a Hindu or an adept of any other eastern religion because Islam is not compatible with eastern religions.
Wahhabis accuse Sufis of inventing new and forbidden teachings and practices and they promote the idea that Sufism originates from eastern religions. This is where this idea comes from.