Abu Burdah said: I heard Abu Musa (may Allah be pleased with him) say many times that the Messenger of Allah (peace and blessings be upon him) said: "When a servant falls ill or is on a journey, his reward is written for him just like the deeds he used to do while resident or while healthy."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6547