Rasarnava 1.41

1.41

durlabhaṃ brahmaniṣṇātaiḥ prāpyate paramaṃ padam
hṛdvyomakarṇikāntaḥstharasendrasya maheśvari //

Difficult to attain even by those proficient in Brahman, the supreme state is attained / through the lord of mercury situated within the pericarp of the heart's ether, O great goddess;