Śatapatha Brāhmaṇa ("of a hundred paths") 2.1.1.10

2.1.1.10

tadyathā śaṅkubhiścarma vihanyāt | evamimām pratiṣṭhām paryabṛṃhanta seyaṃ dhruvāśithilā pratiṣṭhā tasyāṃ dhruvāyāmaśithilāyāmagnī ādadhata tato 'syai sapatnānnirabhajan

Accordingly, in like manner as one would stretch a skin by means of wooden pins, they fastened down this resting-place; and it formed a firm and steady resting-place. And when it was firm and steady, they set up the two fires on it; and thereupon they excluded their enemies from any share in it.