From the article. There are many reasons it may have come about but not for a religious reason nor in the bible.
"The saying God bless you in response to a sneeze is of ancient origin, and there are a variety of stories about where it first came from. The practice of saying, “God bless you,” when someone sneezes does not come from the Bible, nor is there any mention of the practice in the Bible. However, the saying God bless you was used both by Hebrews (Numbers 6:24) and the early Christians as a benediction."
The practice of blessing someone after a sneeze is probably as old as the first century. The origin of the practice is most likely rooted in superstition: the belief that a sneeze is the body trying to rid itself of evil spirits, the thought that the heart stops beating when a person sneezes, or the fear that a sneeze somehow opens the body to evil spirits. In these cases, saying, “God bless you,” was a kind of protection or good luck charm that shielded the sneezer from being invaded by spirits or affected by evil. Other cultures have a similar response to sneezes, believing that a sneeze could signal ill health: they might say, “Salud” (Spanish for “health”) or “Gesundheit” (German for “health”) or “Sláinte” (Irish Gaelic for “good health”) or “Jeebo” (Bengali for “stay alive”).
God Bless You for giving your knowledge of the subject.