bite your tongue!

Bite your tongue! (Be sorry you said that!; Take back what you said!) — Попридержи язык! Возьми свои слова обратно! ~Типун тебе на язык! (контекст)

Example 1: Me a thief? Bite your tongue!

Example 2: Why do you say she will fail? Bite your tongue!

see also
[bite one's tongue]
cf.
[perish the thought]