Śatapatha Brāhmaṇa ("of a hundred paths") 8.6.3.10

8.6.3.10

te cetayamānāḥ | etām punaścitimapaśyaṃstāmupādadhata tadetasyāṃ yonau retaḥ prajātimadadhurmadhyato madhyata evaitadetasyāṃ yonau retaḥ prajātimadadhustathaivaitadyajamāno yatpunaścitimupadadhātyetasyāmevaitadyonau retaḥ prajātiṃ dadhāti madhyato madhyata evaitadetasyāṃ yonau retaḥ prajātiṃ dadhāti

Whilst meditating, they saw this Punaskiti, and put it on (the Gârhapatya), and thereby laid seed and generative power into this womb;--in the centre (they placed it): they thus laid seed and generative power into the very middle of this womb. And in like manner does the Sacrificer now, when he lays down the Punaskiti, lay seed and generative power into this womb;--in the centre (he lays it down): he thus lays seed and generative power into the very middle of this womb.