CHĀNDOGYA UPANISHAD · 6.6.1

दध्नः सोम्य मथ्यमानस्य यो ऽणिमा स ऊर्ध्वः समुदीषति ।
तत् सर्पिर् भवति ॥

dadhnaḥ somya mathyamānasya yo ’ṇimā sa ūrdhvaḥ samudīṣati ।
tat sarpir bhavati ॥

'That which is the subtile portion of curds, when churned, rises upwards, and becomes butter.

F. Max Müller · The Upanishads, Sacred Books of the East 1 (1879)