Ashtangasamgraha 49.73

49.73

yathoktaguṇāyāṃ bhūmau jātāmabālāmajīrṇāṃ śīrṇapurāṇaparṇāmasañjātānyaparṇāṃ tape tapasye vā māse yathoktena vidhinā puṣyayukte candramasi sumuhurte nāgabalāṃ samūlāmuddharet |

tasyā mūlānāṃ tvakpiṇḍamāmramātramakṣamātraṃ vā ślakṣṇapiṣṭamavacūrṇitaṃ vā payasā pibenmadhughṛtābhyāṃ vā lihyāt |

jīrṇe kṣīravṛttireva syāt |

kṣīreṇaiva vā sasarṣiṣkaṃ śāliṣaṣṭikamaśnīyāt |

evaṃ saṃvatsaraprayogādvarṣaśatamajara ityādi samānaṃ pūrveṇa ||

On ground possessing the qualities previously mentioned, in the month of Māgha or Phālguna, when the moon is in conjunction with the constellation Puṣya, at an auspicious moment, according to the prescribed rule, one should dig up a nāgabalā plant along with its root, which is grown, neither too young nor old, its old leaves having fallen off and its new leaves not yet appeared.
One should take a lump of the bark of its roots the size of a mango or the size of an akṣa, finely ground or powdered, and drink it with milk, or lick it with honey and ghee.
When it is digested, one must sustain oneself solely on milk.
Or one may eat boiled śāli or ṣaṣṭika rice with milk and ghee.
By using it thus for a year, one becomes free of old age for a hundred years, and so forth, as stated previously.