Rudra-prasava-varṇana
The Manifestation and Naming of Rudra / Nīlalohita
इत्युक्ते त्वथ तस्यासीच्छरीरस्थं रसात्मकम् / विवेश तत्तदा यस्तु तस्मादापो भवः स्मृतः
ityukte tvatha tasyāsīccharīrasthaṃ rasātmakam / viveśa tattadā yastu tasmādāpo bhavaḥ smṛtaḥ
When this was spoken, the essence of rasa abiding within his body entered into it; and because that rasa entered then, Āpaḥ is remembered as Bhava.