Rule 4 of Elmore Leonard’s 10 Rules for Writing

Elmore Leonard’s 4th Rule of Writing

Never use an adverb to modify the verb ”said” . . .

. . . he admonished gravely. To use an adverb this way (or almost any way) is a mortal sin. The writer is now exposing himself in earnest, using a word that distracts and can interrupt the rhythm of the exchange. I have a character in one of my books tell how she used to write historical romances ”full of rape and adverbs.”

Source: New York Times