Adi Parva - Sambhava Parva 44

"Vaisampayana said, 'Thus asked, the tiger among Munis then answered
those Rishis of ascetic wealth, 'Whom shall I blame for this? In fact,
none else (than my own self) hath offended against me!' After this, O
monarch, the officers of justice, seeing him alive, informed the king of
it. The latter hearing what they said, consulted with his advisers, and
came to the place and began to pacify the Rishi. fixed on the stake. And
the king said, 'O thou best of Rishis, I have offended against thee in
ignorance. I beseech thee to pardon me for the same. It behoveth thee not
to be angry with me.' Thus addressed by the king, the Muni was pacified.
And beholding him free from wrath, the king took him up with the stake
and endeavoured to extract it from his body. But not succeeding therein,
he cut it off at the point just outside the body. The Muni, with a
portion of the stake within his body, walked about, and in that state
practised the austerest of penances and conquered numberless regions
unattainable by others. And for the circumstances of a part of the stake
being within his body, he came to be known in the three worlds by the
name of Ani-Mandavya (Mandavya with the stake within). And one day that
Brahamana acquainted with the highest truth of religion went unto the
abode of the god of justice. And beholding the god there seated on his
throne, the Rishi reproached him and said, 'What, pray, is that sinful
act committed by me unconsciously, for which I am bearing this
punishment? O, tell me soon, and behold the power of my asceticism.'

"The god of justice, thus questioned, replied, 'O thou of ascetic wealth,
a little insect was once pierced by thee on a blade of grass. Thou
bearest now the consequence of the act. O Rishi, as a gift, however
small, multiplieth in respect of its religious merits, so a sinful act
multiplieth in respect of the woe it bringeth in its train.' On hearing
this, Ani-Mandavya asked, 'O tell me truly when this act was committed by
me. Told in reply by the god of justice that he had committed it, when a
child, the Rishi said, 'That shall not be a sin which may be done by a
child up to the twelfth year of his age from birth. The scriptures shall
not recognise it as sinful. The punishment thou hast inflicted on me for
such a venial offence hath been disproportionate in severity. The killing
of a Brahmana involves a sin that is heavier than the killing of any
other living being. Thou shall, therefore, O god of justice, have to be
born among men even in the Sudra order. And from this day I establish
this limit in respect of the consequence of acts that an act shall not be
sinful when committed by one below the age of fourteen. But when
committed by one above that age, it shall be regarded as sin.'

"Vaisampayana continued, 'Cursed for this fault by that illustrious
Rishi, the god of justice had his birth as Vidura in the Sudra order. And
Vidura was well-versed in the doctrines of morality and also politics and
worldly profit. And he was entirely free from covetousness and wrath.
Possessed of great foresight and undisturbed tranquillity of mind, Vidura
was ever devoted to the welfare of the Kurus.'"