Think not in anywise of those killed in the way of the Lord, as if they were dead. Yea, they are alive, and are nourished with their Lord, exulting in that which God hath given them of His favour, and rejoicing on behalf of those who have not yet joined them, but are following after. No terror afflicteth them, neither are they grieved.
To secure the crown of martyrdom, it sufficed to make at the very last moment the simplest and most formal profession of faith in God and Mohammad.
Thus Amir ibn Thabit had up to the day of Ohod, been an open unbeliever. He accompanied the Muslim army and was mortally wounded on the field. His comrades asked him regarding his creed; with his dying breath he whispered in reply that it was for Islam he had fought, and that he believed in God and in his Prophet. When this was told to Muhammad, he blessed his memory, and said that he was already an inheritor of Paradise.
On the other hand, any amount of bravery without such formal profession was of no avail. Thus a Jew named Kozman, who was numbered among the Disaffected, showed incredible valor at Ohod, killing with his own hands seven or eight of Koreish. When expiring on the field, and being congratulated on the prospect of Paradise, he said, with his last breath, that he had been fighting not for the faith, but for his people, and in defense of his native city. Mohammad, when told of it, declared that in spite of his services he was “a child of hell-fire.” Ibn Hisham, P. 578
Page 271 of the book, Life of Muhammad, Sir William Muir