Śatapatha Brāhmaṇa ("of a hundred paths") 13.4.1.12

13.4.1.12

athāgneyīmiṣṭiṃ nirvapati pathaśca kāmāya yajñamukhasya cācambaṭkārāyātho agnimukhā u vai sarvā devatāḥ sarve kāmā aśvamedhe mukhataḥ sarvāndevānprītvā sarvānkāmānāpnavānīti

For the object of (gaining) the road, and in order not to lose the mouth (mukha) of the sacrifice, he then prepares an ishti-offering to Agni. For, indeed, all the deities have Agni for their mouth, and in the Asvamedha are (contained) all objects of desire: 'Having, at the outset (mukhatah), gratified all the gods, may I obtain all my desires!' so he thinks.