The Guru Vandana, Guru Prayer, is from the Guru Gītā in the Skanda-Purāṇa. The Guru Vandana, Guru Prayer is in the Swami Rama Sadhaka Grama Handbook if you have a copy.
ॐ गुरुर्ब्रह्मा गुरुर्विष्णुर्गुरुर्देवो महेश्वरः।
गुरुः साक्षात्परं ब्रह्म तस्मै श्रीगुरवे नमः॥१॥
gurur brahmā gurur viṣṇur gurur devo maheśvaraḥ,
guruḥ sākṣāt paraṁ brahma tasmai śrī-gurave namaḥ.
Guru who is Brahmā [the Creator], Viṣṇu [the Maintainer] and Śiva [the Great Lord through whom all things return to their origin]. To that Guru who is the direct experience of Brahman, salutations.
To hear Swami Rama sing the Guru Vandana, please use this link: https://www.youtube.com/watch?v=a8UcrJ19VCU
What is Brahman?
Swami Rama wrote: “The word Brahman is derived from the Sanskrit verb root bṛha or bṛhi meaning expansion, knowledge, or all-pervasiveness. This word is always of a neuter gender; it represents Absolute Reality beyond the concept of male or female and all other dualities. Brahman is omnipresent, omniscient, omnipotent; it is the very nature of one’s true Self. That Absolute Reality, that Supreme Consciousness, which is never affected by the ever-changing nature of the world, is Brahman. That which alone exists and allows the entire universe to appear within itself is called Brahman. That Brahman is no different from oneself; all of humanity is Brahman. From this point of view, all people are essentially one and the same. Placing duality and diversity within humanity is the greatest loss, and realizing the oneness within and without is the highest gain.”