Mudgalapurana 2.12.15

2.12.15

tamomayaṃ tamaḥsthānaṃ gatyā parvaṇi dhāvati |
chāyayā sūryacandrau vā ācchādayati sattvaram ||

Full of darkness, an abode of darkness, he runs swiftly along his course at the conjunction; / with his shadow, he quickly covers the sun or the moon.