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

Question: If it is not a case of my being attacked, then the thought of killing may be put to rest. If, however, one has been attacked, overcome by force, and is then being coerced by imminent peril, what should one do then?

Reply: One should weigh the relative gravity of the alternatives. If someone is about to take one's life, one should first consider whether the benefit from preserving the precept is more important or whether the benefit from preserving one's physical life is more important and whether breaking the precept constitutes a loss or whether physical demise constitutes a loss.

After having reflected in this manner one realizes that maintaining the precept is momentous and that preserving one's physical life is unimportant. If in avoiding peril one is able only to succeed in preserving one's body, then what advantage is gained with the body? This body is the swamp of senescence, disease and death. It will inevitably deteriorate and decay. If, however, it is for the sake of upholding the precept that one loses one's body, the benefit of it is extremely consequential.

Furthermore, one should consider thus: "From the past on up to the present, I have lost my life an innumerable number of times. At times I have incarnated as a malevolent brigand, as a bird, or as a beast where I have lived merely for the sake of wealth or profit or have engaged in all manner of unworthy pursuits. Now I have encountered a situation where it might be for the sake of preserving the precepts of purity. To not spare this body and to sacrifice my life to uphold the precepts would be a billion times better than and in fact incomparable to safeguarding my body at the expense of violating the prohibitions." In this manner one decides that one should forsake the body in order to protect the integrity of the pure precepts.