Shatapatha Brahmana 13.2.7.10

13.2.7.10

saṃśito apsvapsujā iti apsuyonirvā aśvaḥ svayaivainaṃ yonyā samardhayati brahmā somapurogava iti somapurogavamevainaṃ svargaṃ lokaṃ gamayati

'Trimmed up in the waters was the water-born,'--the horse, indeed, has sprung from the womb of the waters: with its own (mother's) womb he thus supplies it;--'Brahman (m.), with Soma for his leader,'--he thus makes it go to heaven with Soma for its leader.