Shatapatha Brahmana 5.5.1.9

5.5.1.9

atha ya eṣa aindra ekādaśakapālaḥ puroḍāśo bhavati | tasyarṣabho dakṣiṇā sa haindro yadṛṣabho yadyu saumyaścarurbhavati tasya babhrurgaurdakṣiṇā sa hi saumyo yadbabhrustam brahmaṇe dadāti brahmā hi yajñaṃ dakṣiṇato 'bhigopāyati tasmāttam brahmaṇe dadāti

And what cake on eleven potsherds there is for Indra, the fee for that is a bull, for the bull is Indra. And if there be a pap for Soma, then the fee for that is a brown ox, for the brown one is sacred to Soma. He gives it to the Brahman, for the Brahman guards the sacrifice from the south: therefore he gives it to the Brahman.