Śatapatha Brāhmaṇa ("of a hundred paths") 6.7.1.9

6.7.1.9

yadbevoparinābhi | avāgvai nābhe retaḥ prajāpatistejo vīryaṃ rukbho nenme retaḥ prajātiṃ tejo vīryaṃ rukbhaḥ pradahāditi

And, again, why over the navel,--below the navel is the seed, the power of procreation, and the gold plate represents vital energy and vigour: (he does so, thinking,) 'Lest the gold plate burn up my seed, my power of procreation, my vital energy and vigour.'