B'midbar 20:8 shows that G-d instructs Moshe and Aharon to speak to the rock, and it will bring forth water.
Usually, when G-d instructs Moshe to speak to B'nai Yisra'el he indicates what Moshe should tell them. Here, it doesn't seem apparent what G-d wanted Moshe and Aharon to say to the rock. What's missing? What words were they supposed to say?