Sahih Bukhari Volume 008, Book 077, Hadith Number 603.
Narated By Abu Huraira : We witnessed along with Allah's Apostle the Khaibar (campaign). Allah's Apostle told his companions about a man who claimed to be a Muslim, "This man is from the people of the Fire." When the battle started, the man fought very bravely and received a great number of wounds and got crippled. On that, a man from among the companions of the Prophet came and said, "O Allah's Apostle! Do you know what the man you described as of the people of the Fire has done? He has fought very bravely for Allah's Cause and he has received many wounds." The Prophet said, "But he is indeed one of the people of the Fire." Some of the Muslims were about to have some doubt about that statement. So while the man was in that state, the pain caused by the wounds troubled him so much that he put his hand into his quiver and took out an arrow and committed suicide with it. Off went some men from among the Muslims to Allah's Apostle and said, "O Allah's Apostle! Allah has made your statement true. So-and-so has committed suicide." Allah's Apostle said, "O Bilal! Get up and announce in public: None will enter Paradise but a believer, and Allah may support this religion (Islam) with a wicked man."