Halakha Mazmur 15:3: Sefer Chasidim

It is forbidden to kill lice on a table at which you are eating.¹Shulhan Arukh, “Orah Hayim,” 167, Mogen Avraham, note 13. And he who kills lice on it, is as if he killed on the altar, for the table is the altar,²Hagigah 27a. as it is said “and he said unto me: ‘This is the table that is before the Lord’” (Ezek. 41:22). And for this reason we cover knives during the grace, for it is said “For if thou lift up thy sword upon it, thou hast profaned it” (Exod. 20:25). It is forbidden to write in a book “so and so owes me so much and so much.” “And round about Him it stormeth mightily” (Ps. 15:3). From this we learn that the Holy One, blessed be He, deals with the good strictly, even to a hair’s breadth.³Yebamoth 121b. Because Sarah lied about Isaac, “Then Sarah denied, saying, etc.… ” (Gen. 18:15) therefore the circumstance precipitating her death came through Isaac, for her soul took flight and she died when she heard the report of the binding of Isaac.⁴Rashi, Genesis 23:2. The news precipitated her death.