Jami` at-Tirmidhi 28:12

Abu Hurairah narrated (that the the Messenger of Allah (s.a.w)) said:

"Whoever kills himself with (an instrument of)iron, his iron will be in his hand, to continually stab himself in his stomach with it, in the fire of Jahannam, dwelling in that state eternally. And whoever kills himself with poison, then his poison will be in his hand, to continually take it in the Fire of Jahannam, dwelling in that state eternally. And whoever throws himself from a mountain to kill himself, then he will be continually throwing himself in the Fire of Jahannam, dwelling in that state eternally"