God bless you is a common English expression generally used to wish a person blessings in various situations, especially as a response to a sneeze, and also, when parting or writing a valediction. The phrase has been used in the Hebrew Bible by Jews, and by Christians, since the time of the early Church as a benediction, as well as a means of bidding a person. Many clergy, when blessing their congregants individually or as a group, use the phrase "God bless you".
Origins and legends
National Geographic reports that during the plague of CE 590, "Pope Gregory I ordered unceasing prayer for divine intercession. Part of his command was that anyone sneezing be blessed immediately, since sneezing was often the first sign that someone was falling ill with the plague." By CE 750, it became customary to say "God bless you" as a response to one sneezing. The practice of blessing someone who sneezes dates as far back as at least CE 77 in the West, although it is far older than most specific explanations can account for, with non-theistic well-wishing going as far back as 500 BCE on the Indian subcontinent. Some have offered an explanation suggesting that people once held the folk belief that a person's soul could be thrown from their body when they sneezed, that sneezing otherwise opened the body to invasion by the Devil or evil spirits, or that sneezing was the body's effort to force out an invading evil presence. In these cases, "God bless you" or "bless you" is used as a sort of shield against evil. The Irish Folk story "Master and Man" by Thomas Crofton Croker, collected by William Butler Yeats, describes this variation. Moreover, in the past some people may have thought that the heart stops beating during a sneeze, and that the phrase "God bless you" encourages the heart to continue beating. In some cultures, sneezing is seen as a sign of good fortune or God's beneficence. As such, alternative responses to sneezing are the French phrase à vos souhaits, the German word sometimes adopted by English speakers, the Irish word sláinte, the Italian salute, the Spanish salud, the Hebrew laBri'ut or liVriut , the Arabic saha, the Russian bud' zdorov. In Islam the prophet Muhammad instructed Muslims who sneezes to say "الحمد لله" meaning “Thanks to Allah”, and whoever hears them say that should reply "يرحمكم الله" meaning “may Allah have mercy on you“, and the person who sneezed should reply "يهديك الله ويصلح بالك" meaning “May Allah Guide you to the right path and calm your mind”, and for repeated sneezes, they keep replying the same reply for a maximum of three times, by then the reply is changed to "عافاك الله" meaning “May Allah heal you“ and the replies stop. This act in Islam is called "تشميت العاطس". In Persian culture, the response to sneezing is "Afiat Basheh". More often in the old days and out of superstitious nature, sneezing sometimes has been called "sabr =صبر," meaning "to wait or be patient." And when trying to do something or go somewhere and suddenly sneezing, one should stop or sit for a few minutes and then restart. By this act the "bad thing" passes and one will be saved. Meanwhile, an undated story from the Buddha's lifetime, recorded in the Buddhist Vinaya, concerning customs around sneezing is as follows: "Once while giving a talk he sneezed and everyone in the audience called out `Live long!'. This made so much noise that the talk was interrupted. The Buddha then asked the audience: `When 'Live long!' is said after someone sneezes, do they live long or not because of that?' The monks admitted that this was not so. The Buddha agreed and said that therefore, it is not necessary to say `Live long!' each time someone sneezes "
