CHĀNDOGYA UPANISHAD · 3.4.2

ते वा एते ऽथर्वाङ्गिरस एतद् इतिहासपूराणम् अभ्यतपन् ।
तस्याभितप्तस्य यशस् तेज इन्द्रियां वीर्यम् अन्नाद्यं रसो ऽजायत ॥

te vā ete ’tharvāṅgirasa etad itihāsapūrāṇam abhyatapan ।
tasyābhitaptasya yaśas teja indriyāṃ vīryam annādyaṃ raso ’jāyata ॥

Those very hymns of the Atharvâṅgiras (as bees) brooded over the Itihâsa-purâna; and from it, thus brooded on, sprang as its (nectar) essence, fame, glory of countenance, vigour, strength, and health.

F. Max Müller · The Upanishads, Sacred Books of the East 1 (1879)