Śatapatha Brāhmaṇa ("of a hundred paths") 5.3.5.20

5.3.5.20

athainaṃ vāsāṃsi paridhāpayati | tattārpyamiti vāso bhavati tasmintsarvāṇi yajñarūpāṇi niṣyūtāni bhavanti tadenam paridhāpayati kṣatrasyolbamasīti tadyadeva kṣatrasyolbaṃ tata evainametajjanayati

He then makes him (the king) put on garments. There is that one called târpya; therein are wrought all forms of sacrifice: that he makes him put on, with (Vâg. S. X, 8), 'Thou art the inner caul of knighthood (kshatra)!' He thus causes him to be born from out of what is the inner caul (amnion) of knighthood.