During the first Trump-Clinton presidential debate, Clinton said:
He called this woman "Miss Piggy." Then he called her "Miss Housekeeping," because she was Latina. Donald, she has a name. Her name is Alicia Machado.
Trump responded by asking "Where did you find this?", repeating the question three times. However, I'm not aware that Trump made any real attempts to debunk the claim.
I've tried searching for when and where Trump said this, but I couldn't find where it's supposed to have originated from.