Śatapatha Brāhmaṇa ("of a hundred paths") 3.8.2.13

3.8.2.13

sā yā prajñātāśriḥ | tayābhinidadhāti sā hi yajuṣkṛtā medhyā tadyadagraṃ tṛṇasya tatsavye prāṇau kurute 'tha yadbudhnaṃ taddakṣiṇenādatte

He applies that approved edge of his, for that has been made sacrificially pure by a text. That which is the top part of the stalk he puts in his left hand, and that which is the bottom part he takes with his right hand.