Jaiminīya Upaniṣad Brāhmaṇa 1.46.5

1.46.5

ābhūtir annam asya tat
[tac] caturdhā bhavati
tato māsān ardhamāsān ahorātrāṇy uṣaso 'sṛjata
tad asya māsā ardhamāsā ahorātrāṇy uṣaso 'nūpatiṣṭhante /

Power to become, that is his food. It becomes fourfold. From that he created the months, the half-months, the days and nights, and the dawns. The months, the half-months, the days and nights, and the dawns attend upon that of his.