The Messenger of Allah ﷺ said, "Whoever swallows poison and kills himself will keep swallowing it in the fire of Hell, abiding there forever and ever. Whoever kills himself with a piece of iron, his iron will be in his hand, stabbing himself in the belly with it in the fire of Hell, abiding there forever and ever. Whoever throws himself down from a mountain and kills himself will keep throwing himself down in the fire of Hell, abiding there forever and ever."
حدثنا وكيع قال حدثنا الأعمش عن أبي صالح
قال رسول الله ﷺ من تحسى سما فقتل نفسه فهو يتحساه في نار جهنم خالدا مخلدا فيها أبدا ومن قتل نفسه بحديدة فحديدته في يده يتوجأ بها في بطنه في نار جهنم خالدا مخلدا فيها أبدا ومن تردى من جبل فقتل نفسه فهو يتردى في نار جهنم خالدا مخلدا فيها أبدا
Its chain of transmission is sahih. Bukhari related it, 7/18, in the Book of Medicine, chapter on drinking poison, and Muslim, 1/103, no. 175, in the Book of Faith, chapter on the severity of the prohibition against a person killing himself, and Tirmidhi, 4/386, no. 2044, and he graded it sahih, and Nasai, 4/67, in the Book of Funerals, and 1/67, no. 1965, and Darimi, 2/192, in the Book of Blood Money.