CHĀNDOGYA UPANISHAD · 6.7.1

षोडशकलः सोम्य पुरुषः ।
पञ्चदशाहानि माशीः ।
कामम् अपः पिब ।
आपोमयः प्राणो न पिबतो विच्छेत्स्यत इति ॥

ṣoḍaśakalaḥ somya puruṣaḥ ।
pañcadaśāhāni māśīḥ ।
kāmam apaḥ piba ।
āpomayaḥ prāṇo na pibato vicchetsyata iti ॥

'Man (purusha), my son, consists of sixteen parts. Abstain from food for fifteen days, but drink as much water as you like, for breath comes from water, and will not be cut off, if you drink water.'

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