[work] like a (horse|dog|Trojan)

to work exceptionally hard

The phrase "work like a horse" is believed to have originated in the 17th century, and it is a reference to the hard work and endurance of horses, which were commonly used as draft animals during that time. It is used to describe someone who works very hard, often for long hours and with great dedication. It can be used in both personal and professional contexts.

She worked like a trojan to get her degree, studying late into the night and on weekends.
She's been working like a beaver to get her startup off the ground, putting in long hours and sacrificing her weekends.
The construction crew worked like horses to complete the building on time, even working through the night if necessary.
The construction crew worked like slaves to finish the project on time, often working late into the night.
The farmer worked like a horse during the harvest season, putting in long hours to bring in the crops.