Is expiation (kaffarah) obligatory upon a wife who threatened her son with a knife with the intention of frightening and disciplining him?

It is not permissible for a Muslim to point a weapon at his brother, whether seriously or in jest, due to the Prophet's (peace be upon him) prohibition of that. For he said: "None of you should point a weapon at his brother, for he does not know, perhaps Satan may make it slip from his hand, and he would fall into a pit of Hellfire," and "Whoever points a piece of iron at his brother, the angels curse him until he puts it away, even if he is his brother by father and mother." This warning is amplified if the threat is directed at a child, due to its negative psychological effects on them. The mother who did this must seek forgiveness and repent, and use legitimate disciplinary methods, such as non-brutal beating.