Anandakanda 1.24.36

1.24.36

bhūdharīyantramadhyasthaṃ puṭaṃ saptadinaṃ dadet /
tadbhasma śuddhaṃ sevyaṃ syādguñjāmātraṃ tu maṇḍalam //

placed inside a subterranean apparatus, one should give calcination for seven days.
That pure ash should be consumed to the measure of a guñjā for a maṇḍala period.