Vajra Deha in yoga is a body which has attained the strength
of diamond. This is a special type of yogic achievement mentioned in Yoga Sutra.
The human body is made out of five fundamental cosmic elements called
panchabhutas. Out of these, when prithvi (earth element) – responsible for
hardness – attains special dominance, the body can attain the hardness of a
diamond.
Certain gods and goddesses in Hinduism are said to have a
natural body as strong as a diamond, like Garuda divine bird who is the vehicle
of Vishnu.
The nails of Narasimha incarnation of Vishnu are said to be
hard as diamond (vajra nakha).
Vajra Deha is mentioned in Ayurveda treatises as a special
bodily condition that can be attained by the use of specific medicines called the
rasayanas. The body thus treated becomes so strong that no weapon made of any
metal can harm it.
In Hindu religious tradition, on the day of commencement of
lunar year (Ugadi, Chaitra Shukladi and Gudi Padwa), the tender leaves of the
neem tree are mixed with jaggery and consumed by reciting a prayer, which seeks
a life of a full hundred years with a healthy body of diamond strength.
Sage Dadhichi is said to have attained such a body by the
power of penance. Later, the great sage willingly donated his body to make
vajra, the mighty weapon of Indra, the king of Devas.
It is believed that the Buddhist sage and physician
Nagarjuna prepared a mediation for his patron king which made the body king as
strong as diamond.