Now it came to pass, when they spake daily unto him, and he hearkened not unto them, that they told Haman, to see whether Mordecai’s matters would stand: for he had told them that he was a Jew.
One day, when people talked to Haman every day but he didn't listen, they informed him about Mordecai's situation. They did this because Mordecai was a Jew, as he had mentioned it to them.