After the Mabul (deluge/flood), Hashem promised that he would not destroy the world. Yet we know from Tisha Bav and Yom Kippur's "Asarah Harugay Malchus" (“The Ten Martyrs”) poem that when they were going to kill the High Priest, Rabbi Yishmael, the angels exclaimed "Is this the payment for the Torah?", and Hashem says "Quiet or I will return the world to water."
How could Hashem threaten to break a promise?