Volume 4, Book 52, Number 63 :
Narrated by Al-Bara (radiallaahu `anhu)
A man whose face was covered with an iron mask (i.e. clad in armor) came to the Prophet (sallallaahu `alayhi wasallam) and said, “O Allah’s Apostle! Shall I fight or embrace Islam first? “The Prophet (sallallaahu `alayhi wasallam) said, “Embrace Islam first and then fight.” So he embraced Islam, and was martyred. Allah’s Apostle (sallallaahu `alayhi wasallam) said, “A little work, but a great reward.” (He did very little (after embracing Islam), but he will be rewarded in abundance).
This proves that Allah rewards a person in abundance for the littlest of deeds. This is due to His Grace.
This person (mentioned in the hadith) did not offer one prayer, nor did he completed a fast for Allah. He was granted Paradise for his testimony of faith only (and martyrdom eventually). The reason is that he intended to live as a Muslim from that moment on. Were he granted more life, he would’ve prayed and fasted like other Muslims.
P.S. This makes me think how important it was for him to go to the Prophet (sallallaahu `alayhi wasallam) to ask this question. If he didn’t, it would have been a completely different story. O_O