The Prophet (may Allah's peace and blessings be upon him) mentions Allah's bounty and mercy, and that if a Muslim habitually performs a certain good deed while in good health and being at home, and then something occurs to him, such as an illness that makes him unable to do this deed, or a journey that keeps him too busy to do so, or any other excuse, he will get his reward in full, as he used to obtain it for performing this deed while in good health and at home.