Śatapatha Brāhmaṇa ("of a hundred paths") 1.6.3.19

1.6.3.19

tau hocatuḥ | kimāvayostataḥ syāditi yasyai kasyai ca devatāyai havirnirvapāṃstadvām purastādājyasya yajāniti tasmādyasyai kasyai ca devatāyai havirnirvapanti tatpurastādājyabhāgāvagnīṣomābhyāṃ yajanti tanna saumye 'dhvare na paśau yasyai kasyai ca devatāyai nirvapāniti hyabruvan

They both said, 'What (share) shall then be ours?' They replied, 'For whatever deity they shall take out sacrificial food, they shall in the first place offer to you some clarified butter!' Whenever, therefore, they take out sacrificial food for any deity, they in the first place offer two butter-portions to Agni and Soma. This does not take place at the Soma-sacrifice, nor at the animal offering; for they said, 'for whatever deity they take out....'