صحيح البخاري

Narrated Abu Huraira:

We witnessed (the battle of) Khaibar. Allah's Messenger (ﷺ) said about one of those who were with him and who claimed to be a Muslim. "This (man) is from the dwellers of the Hell-Fire." When the battle started, that fellow fought so violently and bravely that he received plenty of wounds. Some of the people were about to doubt (the Prophet's statement), but the man, feeling the pain of his wounds, put his hand into his quiver and took out of it, some arrows with which he slaughtered himself (i.e. committed suicide). Then some men amongst the Muslims came hurriedly and said, "O Allah's Apostle! Allah has made your statement true so-and-so has committed suicide. "The Prophet (ﷺ) said, "O so-and-so! Get up and make an announcement that none but a believer will enter Paradise and that Allah may support the religion with an unchaste (evil) wicked man.