Skandapurana 6.3.111.27

6.3.111.27

ṛgyajuḥsāmavihitaṃ japañjāpyamaharniśam .
dhyāyamāno mahādevaṃ śucirdhamanisaṃtataḥ .. 111.27 ..

chanting day and night the prayers prescribed by the Ṛg, Yajur, and Sāma Vedas, / meditating on Mahādeva, pure, his veins standing out [on his skin].