MN 144 Channovada Sutta: Advice to Channa
The monk Channa is gravely ill and tells the other monks he is going to ‘use the knife’, ie. kill himself. Sariputra and Maha Cunda question him ‘do you regard they eye, eye-consciousness and things cognizable by the mind through eye-consciousness thus “this is mine, this I am, this is myself?” (then the same with the ear, nose, tongue, body and mind).
Channa replies that no, he doesn’t, that he has realised cessation and so will use the knife blamelessly.
They leave him and he kills himself. They ask the Buddha about it and he agrees that Channa was blameless.
In the notes to the Sutra there is an odd bit where it says that Channa over-estimated himself but attained Arahantship on cutting his own throat. He realised that he was still an ordinary person and the shock of it aroused true insight. How could that be known?