BṚHADĀRAṆYAKA UPANISHAD · 6.3.12

एतम् उ हैव सत्यकामो जाबालो ऽन्तेवासिभ्य उक्त्वोव -- अचापि य एनं शुष्के स्थाणौ निषिञ्चेज् जायेरञ् छाखाः प्ररोहेयुः पलाशानीति ।
तम् एतं नापुत्राय वानन्तेवासिने वा ब्रूयात् ॥

etam u haiva satyakāmo jābālo ’ntevāsibhya uktvova -- acāpi ya enaṃ śuṣke sthāṇau niṣiñcej jāyerañ chākhāḥ praroheyuḥ palāśānīti ।
tam etaṃ nāputrāya vānantevāsine vā brūyāt ॥

Satyakâma Gâbâla told the same to his pupils, and said: 'If a man were to pour it on a dry stick, branches would grow, and leaves spring forth.' Let no one tell this to any one, except to a son or to a pupil.

F. Max Müller · The Upanishads, Sacred Books of the East 15 (1884)