Canto 3 -
Araṇya-kāṇḍa
Chapter 11: Rāma Goes to Agastya’s Āśrama
Text 3.11.13

स हि तेपे तपस्तीव्रं माण्डकर्णिर्महामुनिः।
दशवर्षसहस्राणि वायुभक्षो जलाश्रयः॥

sa hi tepe tapas tīvraṁ māṇḍakarṇir mahā-muniḥ
daśa-varṣa-sahasrāṇi vāyu-bhakṣo jalāśrayaḥ

saḥ hi = that famous; tepe = performed; tapaḥ = austerities; tīvram = fierce; māṇḍakarṇiḥ = Māṇḍakarṇi; mahā-muniḥ = and great sage; daśa-varṣa-sahasrāṇi = for ten thousand years; vāyu-bhakṣaḥ = while consuming air; jala-āśrayaḥ = in water.

That famous and great sage Māṇḍakarṇi performed fierce austerities for ten thousand years in water while consuming air.1

Māṇḍakarṇi immersed himself in the waters of the lake that he had created.

1 “While consuming air” means “while consuming nothing but air.”