Śatapatha Brāhmaṇa ("of a hundred paths") 2.6.1.13

2.6.1.13

tadāhuḥ | dvirupabhṛti gṛhṇīyāddvau hyatrānuyājau bhavata iti tadvaṣṭāveva kṛtva upabhṛti gṛhṇīyānnedyajñasya vidhāyā ayānīti tasmādaṣṭāveva kṛtva upabhṛti gṛhṇīyādājyāni gṛhītvā sa punaḥ prācīnāvītī bhūtvā

Here now they say, 'Let him take butter in the upabhrit (by) twice (ladling with the dipping spoon); since there are two after-offerings at this (sacrifice).' Let him, nevertheless, ladle eight times into the upabhrit: let him do so, lest he should depart from the manner of the sacrifice. After ladling out butter, and shifting his cord back to the right shoulder,--