Śatapatha Brāhmaṇa ("of a hundred paths") 1.3.3.6

1.3.3.6

atha saṃnahanaṃ visraṃsayati | prakLptaṃ haivāsya strī vijāyata iti tasmātsaṃnahanaṃ visraṃsayati taddakṣiṇāyāṃ śroṇau nidadhāti nīvirhaivāsyaiṣā dakṣiṇata iva hīyaṃ nīvistasmāddakṣiṇāyāṃ śroṇau nidadhāti tatpunarabhicādayatyabhicanneva hīyaṃ nīvistasmātpunarabhicādayati

He then undoes the band (of the barhis). 'His (the sacrificer's) wife is sure to bring forth without difficulty,' thinking thus he undoes the band. He puts it down on the right hip (of the altar); for this represents his (the sacrificer's) waist-band, and it is on the right side that the waist-band is (tied): this is the reason why he puts it down on the right hip. He again covers it over (with sacrificial grass); for the waist-band also is covered (by the upper garment): for this reason he again covers it.