Musnad Ahmad 30:3065

Waki’ narrated to us, he said: 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 sips poison and kills himself, he will be sipping it in the Fire of Hell, abiding therein eternally, forever. And whoever kills himself with a piece of iron, his piece of iron will be in his hand, stabbing his belly with it in the Fire of Hell, abiding therein eternally, forever. And whoever throws himself down from a mountain and kills himself, he will be throwing himself down in the Fire of Hell, abiding therein eternally, forever."