Devibhagavatapurana 11.21.36

Devībhāgavatapurāṇa 11.21.36

gāyatrīcchando mantrasya yathāsaṅkhyākṣarāṇi ca |
tāvallakṣāṇi kartavyaṃ puraścaraṇakaṃ tathā ||