Narasimhapurana 2.7

2.7

kāṣṭhās triṃśat kalā jñeyā kalās triṃśan muhūrtakam
triṃśatsaṃkhyair ahorātraṃ muhūrtair mānuṣaṃ smṛtam //

Thirty kāṣṭhās are to be known as a kalā; thirty kalās are a muhūrta;
a human day-and-night is remembered as consisting of thirty muhūrtas.