Śatapatha Brāhmaṇa ("of a hundred paths") 10.4.3.13

10.4.3.13

tadyāḥ pariṣritaḥ rātrilokāstā rātrīṇāmeva sāptiḥ kriyate rātrīṇām pratimā tāḥ ṣaṣṭiśca trīṇi ca śatāni bhavanti ṣaṣṭiśca ha vai trīṇi ca śatāni saṃvatsarasya rātrayastāsāmekaviṃśatiṃ gārhapatye pariśrayati dvābhyāṃ nāśītiṃ dhiṣṇyeṣu dve ekaṣaṣṭe śate āhavanīye

Thus the enclosing-stones, supplying the place of nights, are made the (means of) gaining the nights, they are the counterpart of the nights: there are three hundred and sixty of them, for there are three hundred and sixty nights in the year. Of these, he lays twenty-one round the Gârhapatya, seventy-eight round the Dhishnya hearths, and two hundred and sixty-one round the Âhavanîya.