Sufism (or ; ) is a branch of Islam, defined by adherents as the inner, mystical dimension of Islam; others contend that it is a perennial philosophy of existence that pre-dates religion, the expression of which flowered within Islam. Its essence has also been expressed via other religions and metareligious phenomena. A practitioner of this tradition is generally known as a . They belong to different ṭuruq or "orders"congregations formed around a masterwhich meet for spiritual sessions (majalis), in meeting places known as zawiyahs, khanqahs, or tekke. Sufi orders (turuq) may trace many of their original precepts from the Islamic Prophet Muhammad through his cousin and son-in-law Ali ibn Abi Talib, with the notable exception of the Naqshbandi who trace their origins through the first Caliph, Abu Bakr. Prominent orders include Ba 'Alawiyya, Chishti, Rifa'i, Khalwati, Mevlevi, Naqshbandi, Nimatullahi, Oveyssi, Qadiria Boutshishia, Qadiriyyah, Qalandariyya, Sarwari Qadiri, Shadhiliyya and Suhrawardiyya.