ŚVETĀŚVATARA UPANISHAD · 6.22

वेदान्ते परमं गुह्यं पुराकल्पे प्रचोदितम् ।
नाप्रशान्ताय दातव्यं नापुत्रायाशिष्याय वा पुनः ॥

vedānte paramaṃ guhyaṃ purākalpe pracoditam ।
nāpraśāntāya dātavyaṃ nāputrāyāśiṣyāya vā punaḥ ॥

This highest mystery in the Vedânta, delivered in a former age, should not be given to one whose passions have not been subdued, nor to one who is not a son, or who is not a pupil.