Mawlana Masih Allah Khan al-Sherwani1 writes:

“Bay’ah is a pledge to strive to adhere to and execute the esoteric and exoteric actions of Islam. This pledge is also called bay’at al-tariqat, which has been in vogue by authoritative transmission from generation to generation from the earliest era of Islam.

The Messenger of Allah (Allah bless him and grant him peace) had enacted the bay’ah of the Sahabah not only on jihad, but on Islam and the adherence to all the injunctions and practices of Islam. This is established by numerous ahadith.

The bay’ah is enacted by the shaykh by placing the right hand of his disciple into his own right hand. If the group contracting the bay’ah is large, the shaykh uses a length of cloth which each member of the group clasps with his right hand. Women who perform the bay’ah do so from behind a screen. A mahram of the female should be present at the bay’ah ceremony. A length of cloth is spread from the shaykh to the lady behind the screen and the pledge is taken verbally, just as it is proven by the ahadith.

This is the method of bay’ah when one is in the presence of the shaykh. Those who are not able to be present themselves personally to the shaykh may contract the bay’ah by means of a letter or through the agency of a responsible and trustworthy person. This form of bay’ah is called bay’ah al-‘uthmani. The Messenger of Allah (Allah bless him and grant him peace), on the occasion of the Pledge of Ridhwan, took the bay’ah of ‘Uthman (Allah be pleased with him) in his absence. He (Allah bless him and grant him peace) placed his right hand on his own left hand and announced that he had made the bay’ah of ‘Uthman (Allah be pleased with him).”

(Shari’ah wa Tasawwuf, p.100-2)