Markandeyapurana 42.9

42.9

viṣṇur-brahmā-haraścaiva ṛksāmāni yajūṃṣi ca /
mātrāḥ sārdhāśca tistraśca vijñeyāḥ paramārthataḥ //

The syllable Om, consisting of three and a half instants, should be known in its true sense as the three Vedas—the Ṛc, Sāma and Yajus—the three worlds, the three fires, and the three deities Viṣṇu, Brahmā and Śiva. And the yogi, who is absorbed in religious meditation thereon, may obtain extinction therein.