The following story is probably a myth as there are several versions of the dream and its timing. Take this as legend only: 

One afternoon in 1865, President Lincoln's Cabinet entered a council room for a meeting and found the President seated at the head of the table, his face buried in his hands. Presently he raised his head. His face was grave and worn. "Gentlemen," he said, "before long you will have important news."

Someone inquired, "Have you bad news, Mr. President? Is it something serious?"

"I have heard nothing; I've had no news," he replied. "But last night I had a dream. I dreamed I was in a boat, alone. I had no oars, no rudder. I was helpless in a boundless ocean." There was silence for a moment. Then the President added: "I have had that dream many times during the war. And each time, some great battle came within a day or two. Yes, gentlemen, perhaps tomorrow, perhaps in just a few hours, you will have important news."

Five hours later, Abraham Lincoln was assassinated.