Shiva Purana
वैदिकानां द्विजानां च पूजा वैदिकमार्गतः । कर्तव्यानान्यमार्गेण इत्याह भगवाञ्छिवः ४२ ।
Lord Śiva Himself has enjoined that the twice-born shall perform the worship according to the Vedic rites and not by any other means.
english translation
vaidikAnAM dvijAnAM ca pUjA vaidikamArgataH । kartavyAnAnyamArgeNa ityAha bhagavAJchivaH 42 ।
hk transliteration by Sanscript