BṚHADĀRAṆYAKA UPANISHAD · 1.3.8

ते होचुः -- क्व नु सो ऽभूद् यो न इत्थम् असक्तेति ।
अयम् आस्ये ऽन्तर् इति ।
सो ऽयास्य आङ्गिरसो ऽङ्गानां हि रसः ॥

te hocuḥ -- kva nu so ’bhūd yo na ittham asakteti ।
ayam āsye ’ntar iti ।
so ’yāsya āṅgiraso ’ṅgānāṃ hi rasaḥ ॥

Then they (the Devas) said: 'Where was he then who thus stuck to us?' It was (the breath) within the mouth (âsye 'ntar ), and therefore called Ayâsya; he was the sap (rasa) of the limbs (aṅga), and therefore called Âṅgirasa.