Śatapatha Brāhmaṇa ("of a hundred paths") 6.3.1.26

6.3.1.26

te mauñjībhirabhidhānībhirabhihitā bhavanti | agnirdevebhya udakrāmatsa muñjam prāviśattasmātsa suṣirastasmādvevāntarato dhūmarakta iva saiṣā yoniragneryanmuñco 'gnirime paśavo na vai yonirgarbhaṃ hinastyāhiṃsāyai yonirvai jāyamāno jāyate yonerjāyamāno jāyātā iti

They are fastened with halters of reed-grass to guard (Agni) against injury;--Agni went away from the gods; he entered into a reed, whence it is hollow, and whence inside it is, as it were, smoke-tinged: (thus) that, the reed, is Agni's womb, and Agni is these cattle; and the womb does not injure the child. For it is from a womb that he who is born is born: 'from the womb he (Agni) shall be born when he is born,' thus he thinks.