अतीशवागीश्वरकीर्त्योः तारामन्त्रस्य पुरश्चरणविशये केचन वाक्यानि

From Stephan V Bayer’s The Cult of Tara:Magic and Ritual in Tibet

If one consults the Tantra of Tara the Yogini, the author says, it
would seem that little importance is attached to daily purity and so
on; but, according to the long-established tradition of Atisa, it is
best if the practitioner washes .the dwelling, the utensils, and himself with bathing water over which has been recited the “conquering” mantra, if he gives up meat and beer and so on while he is practising the ritual service, and if in short he keeps himself in a condition of bodily purity. He should avoid garlic and onions, which
pollute the strength of his speech, and beer and drugs, which produce drowsiness; he should avoid anything that might cause contamination or distraction, and he should wash himself again and
again with water over which the mantra has been recited. In this
connection, the text recommends the ritual of Bhavabhadra
the practitioner to cleanse away any lapses in his vows. And before
beginning the ritual, he should first determine by an examination
of omens ….

Finally, the handbook talks of the requisite number of recitations
in the ritual service, and our author quotes Candragomin: “Reciting
300,000 or 600,000 or 1,000,000 times, one accomplishes all functions.” And Vagisvarakirti said: “The count for the syllables of the
mantra is 100,000.” Thus the basic measure of ritual service is
100,000 recitations; but it is also held that in this “age of contention”
one should recite four times as much. Drubch’en rinpoch’e said:
“It is said that if one recites the 10-syllable mantra 10,000,000
times, one’s qualities will equal those of the noble Tara herself.”
That is to say, if one completes 10,000,000 recitations, one will have
the power to accomplish all functions and magical attainments. The
oral tradition ascribed to the Chenngawa, however, holds that if the
practitioner devotes himself to a ritual service of 100,000 recitations
he will be unharmed by any impediments; since she is a deity of
active function, it is quick and easy to succeed in her ritual service.
And since there is a great deal of evidence for this position in the
expanded commentaries upon the various histories of Tara, our
author concludes, we may place our belief therein.

Taranatha’s vignette on Amarasimha the Amarakosha’s author

Also the Acarya Amarasimha was a fully ordained monk
as well as the king’s scribe and could also discourse on the
metaphysics of both Mahayana and the Theravada. Supported
by the Tara Tantra, he was able to make the Noble Lady into
his personal tutelary divinity.Having made his abode in the
land of Malava in the west, he taught Abhidharma (Metaphysics)
to about 500 advanced students for about 24 years while
he stayed there, so it is said. All of those 500 students in
attendance on him gained exceedingly pure minds. Once there
was the heretic Naga King known as Lalita in that area and he
suddenly caused a fierce, unbearable rainstorm to fall and the
rain formed a fast-running river like the Yamuna. It drew very
near to the Acarya’s abode and also to many hamlets. The
Acarya prayed to Arya Tara and as a result the water swirled
round to die right of the Acarya’s home and the city of
Utajayana (Ujjain) many times and finally flowed off into
another great river, and only the Naga’s den and a small
Turuska village were carried away. Tara prophesied to him
in the following words, “Compose a work explaining key
terms!” and he wrote the work known as the Amara-kosa,
which to this very day is extremely widely known in India
among Buddhists and non-Buddhists. The king whose scribe
he was is said to have been Vikramaditya.

Despite the anachronism of the mention of Turuṣkas which is an accretion onto the tale of Amarasimha ,Taranatha is probably recording a genuine traditional tale of the lexicographer here genuinely(as transmitted by his Indian informer).