The 19th prohibition is that the one whom the meisis tried to incite is forbidden from saving the meisis if he sees his life is in danger.

The source of this commandment is G‑d's statement,1 "Do not let your eyes pity him."

The explanation of this is: "Since it is written2 'Do not stand still when your neighbor's life is in danger,' one might imply that you may not stand still even for this [meisis]. The verse therefore says,3 "Do not let your eyes pity him."