Short answer
A tariqa (path) is a Sufi order: a chain of teachers going back to the Prophet ﷺ that trains students to purify the heart. The Deobandi elders belonged to the Chishti, Naqshbandi, Qadiri and Suhrawardi orders. Taking bay'ah (a pledge) with a qualified shaykh is a sunnah practice, not an obligation.
Purifying the heart from pride, envy and showing off is fard on every Muslim. Bay'ah with a shaykh who follows the Sharia and Sunnah is sunnah (some say mustahabb), not fard or wajib, and a proven means. Any practice in an order that breaks the Sharia is rejected, however old the order is.
The four schools agree on this.
Explanation
The Prophet ﷺ defined ihsan as worshipping Allah as if you see Him, and the Quran says, "He has succeeded who purifies it" (91:9). Tasawwuf is the discipline of reaching that. A tariqa is a school of that discipline, with its own daily litanies (awrad), methods of dhikr and a chain of teachers (silsila) reaching back through the generations to the Messenger of Allah. See Is Sufism haram?
In South Asia four orders are best known: the Chishti, Qadiri, Naqshbandi and Suhrawardi. The founders of Darul Uloom Deoband took bay'ah with Haji Imdadullah Muhajir Makki, and scholars such as Rashid Ahmad Gangohi and Ashraf Ali Thanawi guided thousands of students in these orders while teaching fiqh and hadith.
What is bay'ah? A pledge to a shaykh to repent, keep to the Sharia and follow his guidance in reforming yourself. The Companions gave the Prophet ﷺ pledges like this, not only for war: "Pledge to me that you will not associate anything with Allah, will not steal, will not commit zina" (Sahih al-Bukhari). Sufi scholars take this as the root of their bay'ah. It is not a pledge of worship, and the shaykh is not a mediator between you and Allah.
Choosing a shaykh. Shah Waliullah and other scholars listed conditions: he knows the Quran, Sunnah and fiqh, practises them, is from a sound chain, turns people toward Allah and away from himself, and does not seek money or fame. If you cannot find one, keep good company, learn the diseases of the heart, and hold to the obligations. Read Islamic meditation (muraqabah) and What is ihsan?
The evidence
Quran, Surah Ash-Shams 91:9-10
قَدْ أَفْلَحَ مَن زَكَّىٰهَا ﴿٩﴾ وَقَدْ خَابَ مَن دَسَّىٰهَا ﴿١٠﴾
He has succeeded who purifies it, And he has failed who instills it [with corruption].
Purifying the soul is the aim of tasawwuf.
Sahih al-Bukhari 50
Sahih... أن تعبد الله كأنك تراه فإن لم تكن تراه فإنه يراك ...
"To worship Allah as if you see Him, and if you do not see Him, He sees you."
Defines ihsan, the goal of the spiritual path.
Sahih al-Bukhari 18
Sahih... بايعوني على أن لا تشركوا بالله شيئا ...
"Pledge to me that you will not associate anything with Allah."
The pledge of obedience and reform that Sufi bay'ah takes as its root.
Where the ruling is recorded
- al-Qawl al-Jamil (Shah Waliullah), Sections on bay'ah and the conditions of the shaykh. Explains that bay'ah is sunnah or mustahabb and lists the conditions of a true shaykh.
- Shariat and Tariqat (Mawlana Ashraf Ali Thanawi), Discussion of the relation between the Sharia and the path. Teaches that the path cannot contradict the Sharia.
Checked by our team. For a more accurate answer to your own situation, consult a scholar. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.