A thorough study of the hadīth literature reveals that there are two broad categories of ahādīth regarding the concept of contagiousness. One set of ahādīth negates this conception while the other alludes to its occurrence. The phrase lā ‘adwā appears in the ahādīth which means that there is no contagion. The Holy Prophet (may peace and greetings be upon him) has also been reported to have eaten meal with a leper ignoring the danger of contagiousness of leprosy. Contrary to it, the Holy Prophet (may peace and greetings be upon him) has also commanded, “firra min al-majdhūmi kamā tafirru min al-asadi”, that is, run away from a leper as you run away from a lion. He has also given clear instruction regarding plague. He forbade entering a plague-stricken land and commanded to stay in the land where this disease had broken out. This instruction should be taken as a preventive measure against plague which is a contagious disease. Both categories of ahādīth seem contrary to each other and demand a detailed insight into this matter in order to remove the apparent contradiction between them.