Musar for Proverbs 3:31

And it is forbidden to make an association with an evildoer for matters of the world, as it is stated (II Chronicles 20:37), “As you have made an association with Ahaziah, the Lord will break up your work.” And it is [also] stated (Proverbs 3:31), “Do not envy a lawless man, or associate with any of his ways.” And our Rabbis, may their memory be blessed, said in Avot DeRabbi Natan (Avot DeRabbi Natan 9:4), “Do not befriend an evildoer even for the matter of a commandment.” And there are many paths of death found in the association with evildoers; and we have already spoken about this iniquity and the severity of its punishment.

And even in fulfilling a commandment it is forbidden to join with the wicked, as it is said: "Do not envy the man of violence and do not choose any of his ways" (Prov. 3:31). And the sages said: "Do not join with the wicked even in fulfilling a command" (Aboth de R. Nathan, chap. a), and many are the ways that lead to death when one is in the companionship of the wicked.