Śatapatha Brāhmaṇa ("of a hundred paths") 3.2.3.17

3.2.3.17

dakṣiṇāmeva diśam | somena prājānaṃstasmātsomaṃ krītaṃ dakṣiṇā parivahanti tasmādāhuḥ pitṛdevatyaḥ soma iti dakṣiṇāṃ hyetena diśam prājānandakṣiṇā hyetasya dik

Through Soma they recognised the southern region: hence, after the Soma has been bought, they drive it round on the south side; and hence they say that Soma is sacred to the Fathers; for through him they recognised the southern region, and to him belongs the southern region.