“The guru is Brahma, the guru is Vishnu, the guru is Shiva; the guru is truly the supreme Brahman, and to him I bow.”
— Adi Shankara[apocryphal] Guru Stotra, verse 17; widely attributed to Shankara in devotional tradition, unlikely to be his composition

Commentary

This verse, from a devotional hymn in praise of the guru, identifies the teacher with the trinity of Brahma, Vishnu, and Shiva and with the supreme Brahman itself. It is among the most recited verses in Hindu practice, and it expresses the conviction that the spiritual teacher is the mediator of liberating knowledge. Sengaku Mayeda and other historians of the Shankara corpus note that the Guru Stotra survives in several versions and that its attribution is uncertain. Eliot Deutsch observes that the reverence for the teacher in Advaita is grounded in the view that knowledge of the Self must be transmitted through a qualified guide. Richard King shows that the institutional emphasis on the guru reflects the development of monastic lineages in the centuries after Shankara. Paul Hacker argued that much of the devotional literature associated with the tradition was composed later and drew on Shankara's authority. The verse is best understood as an expression of the tradition's reverence for its teachers rather than as a text from Shankara's pen.