Sayyiduna al-Bara' (may Allah be pleased with him) said: A man came to the Prophet (peace and blessings be upon him) and said: "I bear witness that there is no god but Allah and that you are His servant and Messenger." Then he fought on the battlefield of jihad until he was martyred, and the Prophet (peace and blessings be upon him) said: "He did little, but he gained much reward."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18541