Śatapatha Brāhmaṇa ("of a hundred paths") 11.8.3.2

11.8.3.2

atho apyāhuḥ saurya evaiṣa paśuḥ syāditi tasmādetasminnastamite paśavo badhyante badhnantyekānyathāgoṣṭhameka upasamāyanti tasmātsaurya evaiṣa paśuḥ syāditi

And they also say, 'To Sûrya (the sun) that victim should belong;'--whence it is that cattle are tied up when he (the sun) has set: some of them they tie up in their respective stables, and others just flock together:--'therefore,' they say, 'it is to Sûrya that this victim should belong.'