From Nagarjuna's Treatise on the Great Perfection of Wisdom
(Dharmamitra Translation)

Question: We are already aware of the characteristics of shiila. What is it that constitutes shiila paaramitaa?

Response: There are those who say that when the bodhisattva upholds the precepts and would rather lose his physical life than damage minor precepts this constitutes shiila paaramitaa. As described in the above-cited Sutra of King Sutasoma, one does not spare even one's own physical life in order to preserve the restrictive precepts. For example, in a former life the Bodhisattva was a greatly powerful poisonous dragon. In the event that any being came to stand before him, in the case of those who were physically weak, if he so much as gazed upon them they would die on the spot. As for those who were physically strong, if he breathed on them, they would die.

This dragon had taken the one-day precepts. He left his dwelling seeking quietude and had gone into the forest. He had been sitting in contemplation for a long time, became tired and lax and then had fallen asleep. It is the way of dragons that when they fall asleep their bodies become in appearance like a snake. His body had patterns on it which were composed of the various colors of the seven precious things. Hunters noticed him and, both startled and delighted, said, "Wouldn't it be appropriate to take this skin which is so rare and difficult to come by and then offer it up to the King of our country that he might use it as an adornment for his robes?" They then held its head down with a staff and used a knife to strip away its skin.

The dragon thought to himself, "My strength is such that, were I only to wish it, turning this entire country upside down would be as easy as turning over one's hand. These people are but little things. How could they be able to put me in difficult straits? Because I am now upholding the precepts I shall have no regard for this body. I should follow along with the words of the Buddha." And so at this time he remained patient, kept his eyes as if asleep, and did not gaze upon them. He held his breath and kept himself from breathing out of pity for these men. For the sake of upholding the precepts he single-mindedly endured the peeling away of his skin and did not develop any thoughts of regret.

Then, having lost his skin, his bare flesh rested directly on the ground. It was in a season where the sun was very hot. He squirmed about in the dirt desiring to make his way to a large body of water. He saw all the little insects coming to eat his body. For the sake of upholding the precepts he did not dare to move any more. He thought to himself, "Now I'll make a gift to the insects of this body. For the sake of the Buddha Way, I will now make a gift of this flesh so as to fill up their bodies. Later, when I have achieved buddhahood, I will employ the giving of Dharma to benefit their minds." After he had made this vow his body dried up and his life was cut off. He was then born in the second of the Traayastri.msha heavens. At that time the poisonous dragon was Shakyamuni Buddha. At this time, the hunters were Devadatta and the six [non-buddhist] masters. The little insects were the eighty thousand gods who gained the Way when Shakyamuni Buddha first turned the wheel of Dharma.