Śatapatha Brāhmaṇa ("of a hundred paths") 3.9.4.20

3.9.4.20

atha yannigrābhamupaiti | yatra vā eṣo 'gre devānāṃ havirbabhūva taddhemā diśo 'bhidadhyāvābhirdigbhirmithunena priyeṇa dhāmnā saṃspṛśeyeti tametaddevā ābhirdigbhirmithunena priyeṇa dhāmnā samasparśayanyannigrābhamupāyaṃstatho evainameṣa etadābhirdigbhirmithunena priyeṇa dhāmnā saṃsparśayati yannigrābhamupaiti

Then as to why he performs the Nigrâbha. Now when he (Soma) first became sacrificial food for the gods, he set his heart on those (four) regions, thinking, 'Could I but consort with those regions as my mate, my loved resort!' By performing the Nigrâbha, the gods then made him consort with the regions as his mate, his loved resort; and in like manner does this (sacrificer) now, by performing the Nigrâbha, make him (Soma) consort with those regions as his mate, his loved resort.