Brhadaranyaka Upanisad (2.4.1): This chapter of the Brhadaranyaka Upanisad (2.4.1 onwards) reveals the nondual vision of the Upanisad by teaching the reality of what is generally taken to be real, satyasyasatyam. Presented in the form of teacher-student dialogues, the Upanishad also shows the method by which this is taught, and what is expected of the student in order to receive this knowledge.
An Audio Course on Vedanta Texts- Upanisad: Brhadaranyaka Upanisad- Bhasyam (2021) by Swami Viditatmananda Saraswati.