fire under

a fire under (someone)

The motivation to take action. Typically used in the phrase like "light/start a fire under (someone)." The deadline really lit a fire under us—we never would have gotten all that work done otherwise. Something must have lit a fire under Jenna—she has really started taking her schoolwork seriously. It's a shame that he got fired, but it might just start a fire under him to look for a job he really loves.
See also: fire
Farlex Dictionary of Idioms. © 2022 Farlex, Inc, all rights reserved.

*fire under someone

Fig. something that makes someone start doing something. (*Typically: build ~; light ~; start ~.) The teacher built a fire under the students, and they really started working. You had better light a fire under your staff. Either that or we will lay off some of them.
See also: fire
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.
See also:
References in classic literature ?
It seems that each green warrior has certain objective points for his fire under relatively identical circumstances of warfare.
Baldia factory was set on fire under a plan, says IO
Fire fighters after the struggle of three hours were able to bring the fire under control after that they started the cooling process with one fire tender to avoid the eruption of fire once again.