eat one's words

eat (one's) words:

Fig. to have to take back one's statements; to confess that one's predictions were wrong.

• You shouldn't say that to me. I'll make you eat your words.
• John was wrong about the election and had to eat his words.

eat your words:

to admit that what you said is wrong

• I may eat my words, but I don't think Holly is going to be able to do this.

.... http://idioms.thefreedictionary.com/eat+words