It is narrated from Hazrat Ubayy bin Ka'b (may Allah be pleased with him) that a man came to the service of the Holy Prophet (peace and blessings be upon him), so the Holy Prophet (peace and blessings be upon him) asked him, "How long has it been since you recovered from Umm Mildam (fever)?" He replied, "I have never had this ailment." The Prophet (peace and blessings be upon him) said, "The example of a Muslim is like that of a grain which is sometimes red and sometimes yellow."