Śatapatha Brāhmaṇa ("of a hundred paths") 3.1.3.1

3.1.3.1

apaḥ praṇīya | āgnāvaiṣṇavamekādaśakapālam puroḍāśaṃ nirvapatyagnirvai sarvā devatā agnau hi sarvābhyo devatābhyo juhvatyagnirvai yajñasyāvarārdhyo viṣṇuḥ parārdhyastatsarvāścaivaitaddevatāḥ parigṛhya sarvaṃ ca yajñam parigṛhya dīkṣā iti tasmādāgnāvaiṣṇava ekādaśakapālaḥ puroḍāśo bhavati

Having brought water forward, he takes out (the material for) a cake on eleven potsherds for Agni and Vishnu; for Agni is all the deities, since it is in Agni that offering is made to all the deities. Moreover Agni is the lower half, and Vishnu is the upper half of the sacrifice: 'I will become consecrated after encompassing all the deities, after encompassing the entire sacrifice,' thus he thinks, and hence there is a cake on eleven potsherds for Agni and Vishnu.