see burn the midnight oil.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
How to use midnight oil in a sentence
The days were all too short, and soon the midnight-oil began to burn.Poppy | Cynthia Stockley
August Niemann, the German novelist, devotes the forenoon to literary work, but never burns midnight-oil on his writing-desk.Methods of Authors | Hugo Erichsen
There are two varieties of college students—the midnight-oil and the natural-gas kind; and Petey was a whole gas well in himself.At Good Old Siwash | George Fitch