Shatapatha Brahmana 13.5.1.14

13.5.1.14

athaitānekaviṃśataye cāturmāsyadevatābhya ekviṃśatimekaviṃśatim paśūnālabhata etāvanto vai sarve devā yāvatyaścāturmāsyadevatāḥ sarve kāmā aśvamedhe sarvāndevānprītvā sarvānkāmānāpnavānīti na tathā kuryāt

Then those (victims) for the twenty-one (stakes). He seizes twenty-one animals for each of the (eleven) deities of the Seasonal offerings; for as many as there are gods of the Seasonal offerings so many are all the gods; and all objects of desire are in the Asvamedha: 'by gratifying all the deities I shall gain all my desires,' so he thinks. But let him not proceed in this way.