Śatapatha Brāhmaṇa ("of a hundred paths") 1.8.3.13

1.8.3.13

sa vā agraṃ juhvāmanakti | madhyamupabhṛti mūlaṃ dhruvāyāmagramiva hi juhūrmadhyamivopabhṛnmūlamiva dhruvā

He anoints the top (of the prastara with the butter) in the guhû, the middle part (with that) in the upabhrit, and the lower end (with that) in the dhruvâ; for the guhû is, as it were, the top, the upabhrit the middle, and the dhruvâ the root.