Daniel Chapter 2 Vs. 9

Nebuchadnezzar's Dream

But if ye will not make known unto me the dream, there is but one decree for you: for ye have prepared lying and corrupt words to speak before me, till the time be changed: therefore tell me the dream, and I shall know that ye can shew me the interpretation thereof. Dan. 2:9

But if ye... He again referred to the penalty (cf. Dan. 2:5) for failure to tell him the dream.

till the time... He felt that the only way he could trust their interpretation of the future was by having them first recall his dream. Otherwise he would conclude that they were conspiring to tell him misleading and wicked things.

I shall know... Also Nebuchadnezzar may have become impatient with the wise men who were presumably older than he as he had inherited them from his father. Another reason for the test may have been that he was suspicious of their claims to wisdom.