Abu Hurairah reported,

We were present at Khaybar, and the Messenger of Allah ﷺ said about one of the men with him who claimed to be a Muslim, "This man is among the people of the Fire."When the battle began, the man fought fiercely, sustaining many wounds, so much so that some people began to have doubts. Then, overcome by the pain of his wounds, the man reached for his quiver, drew out some arrows, and stabbed himself to death.Some men from among the Muslims rushed to the Prophet and said, "Messenger of Allah, Allah has confirmed the truth of your words. So-and-so killed himself by his own hand."He said, "Stand up, so-and-so, and announce that none shall enter Paradise except a believer. Indeed, Allah supports this religion even through a wicked man."

عن أبي هريرة قال

شهدنا خيبر، فقال رسول الله ﷺ لرجل ممن معه يدعي الإسلام: هذا من أهل النار. فلما حضر القتال قاتل الرجل أشد القتال، حتى كثرت به الحراحة، فكاد بعض الناس يرتاب، فوجد الرجل ألم الجراحة، فأهوى بيده إلى كنانته، فاستخرج منها أسهما، فنحر بها نفسه، فاشتد رجال من المسلمين، فقالوا يا رسول الله، صدق الله حديثك، انتحر فلان فقتل نفسه، فقال: قم يا فلان فأذن أنه لا يدخل الجنة المؤمن، إن الله يؤيد الدين بالرجل الفاجر.