Is it true that whoever brandishes a knife at his brother will find the victim dead after forty days?

There is no truth to the circulating saying. However, it is authentically reported that the Prophet, peace and blessings be upon him, forbade terrifying a Muslim or pointing a weapon at their face without right, and he threatened anyone who does so with expulsion from Allah's mercy. As stated in the Hadith: "Whoever points an iron implement at his brother, the angels curse him until he puts it down," and "It is not lawful for a Muslim to frighten another Muslim."