Sahih Bukhari

Narrated Al-Bara:A man whose face was covered with an iron mask (i.e. clad in armor) came to the Prophet (ﷺ) and said, ""O Allah's Messenger (ﷺ)! Shall I fight or embrace Islam first? ""The Prophet (ﷺ) said, ""Embrace Islam first and then fight."" So he embraced Islam, and was martyred. Allah's Messenger (ﷺ) said, A Little work, but a great reward. ""(He did very little (after embracing Islam), but he will be rewarded in abundance