स एतां त्रयीं विद्यामभ्यतपत्तस्यास्त-ध्यमानाया रसान्प्राबृहद्भूरित्यृग्भ्यो भुवरिति यजुर्भ्यः स्वरिति सामभ्यः ॥ ३ ॥
In plain words
He meditated deeply upon the threefold Veda. As it was heated by this concentration, he extracted its subtle essences: 'Bhūḥ' from the Ṛgveda, 'Bhuvaḥ' from the Yajurveda, and 'Svaḥ' from the Sāmaveda.
Close to the Sanskrit
He concentrated intensely on this threefold Veda. From it, as it was being heated, he drew forth the essences: 'Bhūḥ' from the Ṛg verses, 'Bhuvaḥ' from the Yajus formulas, 'Svaḥ' from the Sāman chants.