Śatapatha Brāhmaṇa ("of a hundred paths") 3.2.1.9

3.2.1.9

sa vai jaghanārdha ivaivāgra āsīta | atha yadagra eva madhya upaviśedya enaṃ tatrānuṣṭhyā hareddrapsyati vā pra vā patiṣyatīti tathā haiva syāttasmājjaghanārdha ivaivāgra āsīta

He must indeed sit down first on the hind part (of the skin). Were he, on the other hand, to sit down at once in the middle (of the skin), and were any one there to curse him, saying, 'He shall either become demented or fall down headlong!' then that would indeed come to pass. Let him therefore first sit down on the hind part (of the skin).