Vayupurana 1.23.44

Vāyupurāṇa 1.23.44

rahasyaṃ sarvamantrāṇāṃ pāvanaṃ puṣṭhivarddhanam.
śrṛṇuṣvaitatparaṃ guhyamādisarge yathā tatham .. 23.42 ..