There is a widespread belief that if a Torah scroll is dropped, both the person who was carrying it and those who witnessed the mishap are obliged to fast for 40 days. However, while dropping a Torah scroll is considered a serious infraction and sometimes is followed by a fast (typically for a day, from sunrise to sunset), there is little in Jewish sources to support this idea.
Nothing in classical Jewish legal sources requires fasting when a Torah is dropped, let alone fasting for 40 days. The Talmud (Moed Katan 26a) notes that one must tear clothing, a mourning custom known as kriah, when a Torah scroll is burned, a ruling later codified in the Shulchan Aruch. Given that 40 days of fasting is a more severe response than rending one’s clothing, and that dropping a Torah is less severe than burning a Torah, it’s hard to square the halachic requirement of kriah for a burnt scroll with the notion that one ought to fast for 40 days if a Torah is merely dropped.
References to the custom of fasting in response to a fallen Torah scroll arose much later, but none stipulate that the fast should last for 40 days. According to Rabbi David Golinkin, the custom was first mentioned in 1662 by the Italian kabbalist Rabbi Moshe Zacuto, and was likely established as a custom by the 17th-century Polish talmudist Rabbi Abraham Gombiner. The Kitzur Shulchan Aruch, an abbreviated version of the longer Shulchan Aruch published in the 19th century, rules that if a scroll falls from someone’s hand, the person who dropped it and anyone who witnessed it must fast. But there is no mention of a 40-day fast.
Some have suggested that the idea of a 40-day fast corresponds to the 40 days Moses spent receiving the Torah on Mount Sinai. Fasting for an equivalent amount of time would satisfy the principle in religious law known as midah k’neged midah — literally “measure for measure,” or the idea that a punishment must correspond to the crime.
Notwithstanding its cloudy origins, a 40-day fast is widely assumed to be the result of a dropped Torah. A 2012 article in the Wall Street Journal about the custom of hagbah quoted numerous people expressing concern about the 40-day fasting requirement should they drop the scroll. One Chicago community mentioned in the story had “dozens of members” fast from sunrise to sunset for 40 days after a scroll fell from the ark on the High Holidays. An Orthodox community in Massachusetts where a Torah carrier tripped and fell in 2007 opted for a single fast day along with prayer and charitable giving.