Chandogya Upanishad
atha ye 'syodañco raśmayas tā evāsyodīcyo madhunāḍyaḥ atharvāṅgirasa eva madhukṛtaḥ itihāsapurāṇaṃ puṣpam tā amṛtā āpaḥ
The northern rays of the sun are the honey-cells on the left. The (hymns of the) Atharvângiras are the bees, the Itihâsa-purâna (the reading of the old stories) is the flower, the water is the nectar.
te vā ete 'tharvāṅgirasa etad itihāsapurāṇam abhyatapan tasyābhitaptasya yaśas teja indriyaṃ vīryam annādyaṃ raso 'jāyata
Those very hymns of the Atharvângiras (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.
tad vyakṣarat tad ādityam abhito 'śrayat tad vā etad yad etad ādityasya paraḥkṛṣṇaṃ rūpam
That flowed forth, and went towards the sun. And that forms what we call the extreme dark (parah krishnam) light of the sun.