Vṛṣṇivaṃśa–Anukīrtana (Enumeration of the Vṛṣṇi Lineage) — Questions on Viṣṇu’s Human Descent
गर्भो ऽश्मसंभवो ज्ञेयो द्वितीयो राशिरुच्यते / शुक्रं सोमात्मकं विद्यादार्त्तवं पावकात्मकम्
garbho 'śmasaṃbhavo jñeyo dvitīyo rāśirucyate / śukraṃ somātmakaṃ vidyādārttavaṃ pāvakātmakam
Know the embryo (garbha) to arise from aśma, the dense, stone-like principle; this is called the second rāśi. Understand śukra as Soma-natured, and ārtava as Pāvaka-natured (Agni).