‘The Simile of the Mountain’, in Saṃyutta Nikāya 3:25:

[Buddha:] “What do you think, great king? Suppose a man would come to you from the east, one who is trustworthy and reliable, and would tell you: ‘For sure, great king, you should know this: I am coming from the east, and there I saw a great mountain high as the clouds coming this way, crushing all living beings. Do whatever you think should be done, great king…’”

“If, venerable sir, such a great peril should arise, such a terrible destruction of human life, the human state being so difficult to obtain, what else should be done but to live by the Dhamma, to live righteously, and to do wholesome and meritorious deeds?”

“I inform you, great king, I announce to you, great king: aging and death are rolling in on you. When aging and death are rolling in on you, great king, what should be done?”

“As aging and death are rolling in on me, venerable sir, what else should be done but to live by the Dhamma, to live righteously, and to do wholesome and meritorious deeds?"¹

Bostrom, ‘The Fable of the Dragon Tyrant’:

Once upon a time, the planet was tyrannised by a giant dragon. The dragon stood taller than the largest cathedral, and it was covered with thick black scales. Its red eyes glowed with hate, and from its terrible jaws flowed an incessant stream of evil smelling yellowish green slime. It demanded from humankind a blood curdling tribute: to satisfy its enormous appetite, ten thousand men and women had to be delivered every evening at the onset of dark to the foot of the mountain where the dragon tyrant lived. Sometimes the dragon would devour these unfortunate souls upon arrival; sometimes again it would lock them up in the mountain where they would wither away for months or years before eventually being consumed… (p. 273)

The general ethical argument in the fable is simple: there are obvious and compelling moral reasons for the people in the fable to get rid of the dragon. Our situation with regard to human senescence is closely analogous and ethically isomorphic to the situation of the people in the fable with regard to the dragon. Therefore, we have compelling moral reasons to get rid of human senescence. (p. 277)