A khirqa is a wool cloak, often patched (muraqqa˓a). Sufis wore the khirqa as a sign of having embarked on the Sufi path from at least the eighth century. By the eleventh century Sufis had developed ways of transmitting spiritual knowledge and authority: Sufi authors describe the binding of a disciple to a master through an oath (the akhdh al-˓ahd or the bay˓a), becoming part of the master's spiritual chain of authority (silsila), the inculcation (talqin) of a method of prayer (dhikr), and the bestowal of the khirqa from a master to a disciple. Investiture with the khirqa had an initiatic aspect. A disciple could be given the khirqa at the beginning of his training with a shaykh, in which case the khirqa indicated that the disciple had been invested with the means necessary for progressing along the path. The bestowal of a khirqa could certify that the novice had been trained by a master who could attest to his spiritual fitness and preparedness. The silsila and the khirqa served the same purposes as the chain of authority (isnad) and the certificate of permission (ijaza) in ulema circles: They certified that the Sufi had studied and trained under an authoritative master, whose spiritual pedigree could be traced back to the Prophet, and they gave him the authority to transmit a particular spiritual way.
Schimmel, Annemarie. Mystical Dimensions of Islam. Chapel Hill, N.C.: University of North Carolina Press, 1975.