Anandakanda 1.9.34

1.9.34

mardayejjārayedevaṃ tataḥ sūtasya māraṇam /
samūlāṃ kumbhim ādāya gavāṃ mūtreṇa peṣayet //

Thus one should grind and cause it to consume; thereafter is the killing of quicksilver:
Taking kumbhī along with its roots, one should pound it with cow's urine.