Musnad Ahmad 30:330

Abu Mu'awiyah narrated to us, al-A'mash narrated to us, from Abu Salih, from Abu Hurairah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever kills himself with a piece of iron, his piece of iron will be in his hand, stabbing himself with it in the fire of Hell, remaining therein eternally, forever. And whoever kills himself with poison, his poison will be in his hand, sipping it in the fire of Hell, remaining therein eternally, forever. And whoever throws himself from a mountain and kills himself, he will be throwing himself down in the fire of Hell, remaining therein eternally, forever."