Śatapatha Brāhmaṇa ("of a hundred paths") 6.4.2.2

6.4.2.2

athainam parigṛhṇāti | abhryā ca dakṣiṇato hastena ca hastenaivottaratastvāmagne puṣkarādadhyatharvā niramanthatetyāpo vai puṣkaram prāṇo 'tharvā prāṇo vā etamagre 'dbhyo niramanthanmūrdhno viśvasya vāghata ityasya sarvasya mūrdhna ityetat

He then takes hold of it with the (right) hand and spade on the right side; and with the (left) hand on the left side, with, 'From the lotus Atharvan churned thee forth,'--the lotus doubtless means the waters, and Atharvan is the breath; and the breath indeed churned him (Agni, the fire) out of the waters at first;--'from the head of every offerer,'--that is, 'from the head of this All (universe).'