To understand more about the relics, please read existing
threads such as:
Shariras/she li zi/relics
A translated article (by me, so
pardon the poor translations) from Fa Yu Bing Fen (Book 1), Jen
Chen Buddhist Book Publisher
Discussing about Shariras
By Venerable
Shen-Kai

The Sharira is truly a very amazing and miraculous object. Though
it is a material substance, it can also be said to be immaterial.
However, only the Buddhas, Bodhisattvas, great Masters, saints and
Bhikshus would have shariras. Some lay Buddhists who are great
practitioners, both males and females, may also have shariras.
Typically, after the practitioner passes away and is cremated,
numerous colourful bead-like objects, known as shariras, would be
retrieved from the ashes. It does not melt under high temperature,
does not dissolve with high humidity, does not spoil under high
pressure, and does not get destroyed over kalpas. Interestingly,
not every Buddhist has shariras. Buddhists who do not practice,
just as other people who do not believe in Buddhism, would not have
shariras. There are plentiful religions in the world. Why is it
that the religious leader, missionaries and believers do not have
shariras? There are also practitioners from religions other than
Buddhism, yet only people who practice the Dharma have shariras.
Besides, one could also tell the level of practice through the
number of shariras produced. Those with deeper level of practice
would have more shariras, while those with a shallow level of
practice would have fewer shariras. If one has practiced for
countless lifetimes, the number of shariras one would have the
beauty of its colour and luster and other miraculous occurrences
would be even more incredible.

According to the records of the life story of Buddha, when
Shakyamuni Buddha entered Nirvana, At this moment, the golden
coffin ascended to the height of seven duo luo trees, moved
around in space, dissolved into the fire of Samadhi,
instantaneously producing ashes and shariras appeared, like
multi-coloured beads, bright and firm. According to the
explanations, there are as many as 84 dou3 shariras. At that
time, the shariras were divided amongst the 8 great Kings and other
Buddhas disciples. They built stupas to venerate the shariras.
While the majority of the shariras were left in the human realm,
some were kept in the Naga realm or Heaven realm. There was also
Buddhas great disciple, Venerable Ananda. When he entered Nirvana,
his physical body levitated to the space, dissolved into fire and
self-cremated. His shariras rained down from the sky upon the banks
of the Ganges river. All these did not only happen in the ancient
times. Even as recent as the great Buddhist leader Master
Tai-Hsu, when he passed away, there were more than 400 shariras.
The Pure Land master Venerable Yin Kwang, also produced a few
hundred shariras when he passed away. There are also other
innumerable great Masters and Teachers who had shariras. There was
especially a Zhang Jia Rinpoche who passed away in Tai Pei in 1957;
he had as many as 7000 to 8000 shariras. He even had the most
precious Vajra gem and six-syllable mantra. The shariras could be
as large as beans and as tiny as seeds. They were very colourful,
but the white ones were especially remarkable. Other than these,
there are also uncountable accounts of Bhikshus, Bhikshunis, lay
male and female Buddhists who passed away with shariras.

Actually, one need not to have shariras only upon ones Nirvana.
For example, one of the greatest disciples of the Buddha
Mahakashyapa, his indestructible body sharira is presently
concealed in the ling2 jiu1 shan1. He would await for the descent
of the Maitreya Buddha, when he would appear in the Dharma
assembly, benefit sentient beings and then enter into Nirvana.
Other examples include the Ksitigarbha Bodhisattva of the Jiu Hua
Mountain in An Hui; Tang Dynasty 6th Zen Patriarch Hui Neng of Cao
Xi; the Ming dynasty Great Master Han Shan; Chinas Wu Jin Zang
Bhikshuni etc, their body sharira are being venerated at Guang Dong
in the Nan Hua monastery. There is also a Venerable in Thailand
who entered Nirvana in his middle age, but his body did not decay,
it is situated at Cheng Niang and the Thais venerate his Body
Relic; it is also known that his hair is grew 5 times longer than
when he was alive. In Taiwan Si Zhi Maitreya Monastery, the Ci Hang
Bodhisattva non-decayed Body Relic was a breaking news, people from
local and abroad pay homage to it; in Nan Hai Pu Tuo Mountain Gu
Fuo Dong, there are many body relics of old monks who passed away
for plenty of years. Regarding body relics/shariras, there are
plenty of cases in different places and mountains in China. Those
who follow and practice (xiu1 chi2) according to the Buddhadharma,
not only bone marrows, even nails, blood, flesh and teeth, the
entire body can become relics, just like there are lights and
colours on [??]s head. Venerable Jiu Mo Luos tongue did not burn
in cremation, these are Sharira Gems.

Sharira can also be obtained through Gan3 Ying4
(induction/invocation), in our country (Taiwan) during the era of
Dong Wu Sun Quan, after hearing that Venerable Fan Zeng Kang Zeng
Kai said the merits of paying homage to shariras, thought of
wanting to pay homage to shariras, therefore requested that
Venerable to sincerely pray. After 49 days, he suddenly heard
sounds coming from the empty bottle, and discovered
Gong-De-She-Li (merits sharira). After trying to hit it with a
hammer on a metal zhuan, the sharira remains undamaged. During the
Song dynasty, lay disciple Wang Ri Xi was carving a Pure Land
scripture on the wooden plank and a sharira was carved out. Again
in Song Dynasty, there was a lady who always recited Amitabha
Sutra, in the sutra suddenly a lot of shariras appeared. During Xi
Pu era, there was a monk called Hui Da, in [??], bowed and
sincerely prayed for Buddhas relic, suddenly the relic rolled out
from the ground, it is now venerated at Ning Bo Ah Yu Wang
monastery, is known to be the relic that Venerable Hui Da prayed
for. Recently there is a General, once he was at Xi-An Xi-Jiao
Monastery [??] stupa, he sincerely prayed and a huge brick fell out
from the top of the stupa, and realized that two shariras are on
top of it, therefore he renovated the stupa. In Hong Kong,
Venerable Lan Mo went to India for Buddhist pilgrimage, in Buddhas
pre-enlightenment Bodhigaya; he met an old practitioner, called
Guang Qing Shi. He was at Jia ? Great Stupa venerating Buddhas
relics for 3 years already, once he witnessed sharira dropping by
itself from the top of the stupa, and it even gave him and another
lay disciple 2 shariras; it was very colourful and lovely. During
Ming Guo, Zheng Jue Sheng old lay disciple once venerated two of
Living Buddha Ban Chans shariras; it automatically multiplied to 7
of them. When Mr Qu Lao passed away, his wife took 2 shariras and
put onto his mouth. When his funeral was over, it was found that
that 7 shariras remain at home. Later it was given to Li Zi Kuan
old lay disciple who is at Taipei Shan Dao monastery for offering,
but realized the sharira has multiplied to 10. In Tibetan Vajrayana
Yellow Hat sect leader Lama Tsongkapa dropped a tooth in his latter
years, his disciples treated it as a sharira and venerated it,
shariras grew out from the tooths root canal. It was distributed
among masses for veneration, after distributing it grew again,
after growing it was distributed again. It was known that there is
a Living Buddha, in the early years at China Mainland before his
passing away, often there are disciples praying/requesting his
sharira, he could at any time drop 2 shariras from his nostrils and
gave them for veneration. It was also heard that there is a
merchant, Da Pu Tuo and Bo Li Jia brothers, they used a jade box
and carried back eight of Buddhas hair strands (also Buddhas
sharira).