At least a few prominent writers share the common belief that you should stop writing while you still have more to give, when you know what to write next. 

3 references:

"You always stop when you know what is going to happen next ... You write until you come to a place where you still have your juice and know what will happen next and you stop and try to live through until the next day when you hit it again." - Ernest Hemingway

"I don't believe in draining the reservoir, do you see? I believe in getting up from the typewriter, away from it, while I still have things to say." - Henry Miller

"Picking up where he left off the previous evening -- he always made sure to stop writing when he knew what would come next, making it easier to begin the next day" - Mason Currey on the writing routine of Kingsley Amis