Proverbs 29:24

24 The accomplices of thieves are their own enemies; they are put under oath and dare not testify.

Read Proverbs 29:24 Using Other Translations

Whoso is partner with a thief hateth his own soul: he heareth cursing, and bewrayeth it not.
The partner of a thief hates his own life; he hears the curse, but discloses nothing.
If you assist a thief, you only hurt yourself. You are sworn to tell the truth, but you dare not testify.