Śatapatha Brāhmaṇa ("of a hundred paths") 3.8.2.17

3.8.2.17

kārṣmaryamayyau vapāśrapaṇyau bhavataḥ | yatra vai devā agre paśumālebhire tadudīcaḥ kṛṣyamāṇasyāvāṇnedhaḥ papāta sa eṣa vanaspatirajāyata tadyatkṛṣyamāṇasyāvāṅapatattasmātkārṣmaryastenaivainametanmedhena samardhayati kṛtsnaṃ karoti tasmātkārṣmaryamayyau vapāśrapaṇyau bhavataḥ

The two omentum-spits are made of kârshmarya wood. For when the gods in the beginning seized (slew) a victim, then, as it was drawn upwards, its sacrificial essence flowed downwards, and from it sprang a tree; and because it flowed down from the (victim) as it was drawn (karsh) upwards, therefore (it became) a kârshmarya tree. With that same sacrificial essence he now perfects it, and makes it whole; therefore the two omentum-spits are of kârshmarya wood.