Ashtangasamgraha 49.75

49.75

tatra sāravṛkṣāṇāṃ sarveṣāṃ svarasārthī kuṣṭhacikitsite khadirakalpamīkṣeta |

ārdravṛkṣāsambhave tu sāraśakalānidvyaṅgulatryaṅgulāni tanūni caturguṇembhsyā plāvyātape trirātraṃ sthāpayet |

tatastānyuddhṛtyānyāni tatra kṣipet |

trirātrācca punaranyānyevaṃ navarātreṇa triḥprakṣepaṇoddhāreṇa ca svarasaḥ parikalpito bhavati ||

Among those, whoever desires the fresh juice of all the heartwood trees should look to the khadira preparation in the treatment of kuṣṭha.
When fresh trees are not available, one should submerge thin chips of the heartwood measuring two or three finger-breadths into a fourfold quantity of water, and keep it in the sun for three nights.
Then, having removed them, one should cast others in there.
And after three nights, others again; in this way, over nine nights, by casting in and removing thrice, a substitute for fresh juice is prepared.