Skandapurana 5.108.23

5.108.23

tasmātsarvaprayatnena kīrtanīyā vicakṣaṇaiḥ ..
kālatraye'pi śucibhirviśeṣācchivadīkṣitaiḥ .. 23 ..

Therefore, it should be recited with every effort by the wise, / who are pure, at the three junctions of the day, especially by those initiated into the rites of Śiva. (23)