Shivapurana 7.2.28.9

Śivapurāṇa (complete text) 7.2.28.9

āṣāḍhe cottarāṣāḍhe pavitrāropaṇaṃ tathā |
śrāvaṇe prākṛtānyāpi maṇḍalāni prakalpayet ||