Shivapurana 7.2.21.14

Śivapurāṇa (complete text) 7.2.21.14

āgneyaṃ vātha vā māntraṃ kuryāt snānaṃ śivena vā |
śivacintāparaṃ snānaṃ yuktasyātmīyamucyate ||