Chandogya Upanishad 6.40

अशनापिपासे मे सोम्य विजानीहीति यत्रैतत्पुरुषोऽशिशिषति नामाप एव तदशितं नयन्ते तद्यथा गोनायोऽश्वनायः पुरुषनाय इत्येवं तदप आचक्षतेऽशनायेति तत्रितच्छुङ्गमुत्पतितँ सोम्य विजानीहि नेदममूलं भविष्यतीति ॥ ३ ॥

6.8.3 — ashanapipase me somya vijanihiti yatraitatpurusho'shishishati namapa eva tadashitam nayante tadyatha gonayo'shvanayah purushanaya ityevam tadapa aachakshate'shanayeti tatritachchhungamutpatitan somya vijanihi nedamamulam bhavishyatiti || 3 ||

'Learn from me, my son, what are hunger and thirst. When a man is thus said to be hungry, water is carrying away (digests) what has been eaten by him. Therefore as they speak of a cow-leader (go-nâya), a horse-leader (asva-nâya), a man-leader (purusha-nâya), so they call water (which digests food and causes hunger) food-leader (asa-nâya). Thus (by food digested &c), my son, know this offshoot (the body) to be brought forth, for this (body) could not be without a root (cause).

'हे सौम्य, मुझसे अशन (क्षुधा) और पिपासा का रहस्य जान। जब पुरुष को "अशिशिषति" (खाने की इच्छा) होती है, तब खाया हुआ (अन्न) जल ले जाता है। जैसे गोनाय, अश्वनाय, पुरुषनाय — वैसे ही जल को "अशनाय" (अन्न-नायक, क्षुधा) कहते हैं। हे सौम्य, जान कि यह शरीर-रूपी शाखा यों उत्पन्न हुई है — यह बिना मूल के नहीं हो सकती।'