Dīkṣā-bhedaḥ (Types of Initiation) — Lalitopākhyāna: Hayagrīva–Agastya Dialogue
गुरुं हुङ्कृत्य तुङ्कृत्य विप्रं वादैर्विजित्य च / विकास्य गुह्यशास्त्राणि भवन्ति ब्रह्मराक्षसाः
guruṃ huṅkṛtya tuṅkṛtya vipraṃ vādairvijitya ca / vikāsya guhyaśāstrāṇi bhavanti brahmarākṣasāḥ
He who cries “huṃ” and “tuṃ” at the Guru, defeats a brāhmaṇa by disputation, and lays open the secret śāstras—such a one becomes a Brahma-rākṣasa.