Abigail Adams' warning to her husband can be seen as prophetic because it predicts an uprising among women. You can argue that this prediction came true with the movements for women's suffrage (beginning in 1848) and for greater rights for women (beginning largely in the 1960s).
In her letter to her husband, Adams warns that, if he and the other lawmakers do not "Remember the Ladies," the women will be "determined to foment a Rebellion." Of course, she was wrong about this in the short term. Women were not given much in the way of rights and still did not rebel. However, beginning in the 1840s, women did start to push for rights. Because they did this, we can argue that Abigail Adams' warning was prophetic.