hard at

hard at (something)

 and hard at doing something
working hard at something. Tom's busy. He's hard at work on the lawn.
See also: hard
References in classic literature ?
I told him, that as he worked so hard at bogging, he required thick boots and stout clothing, which yet were soon soiled and worn out, but I wore light shoes and thin clothing, which cost not half so much, though he might think that I was dressed like a gentleman (which, however, was not the case), and in an hour or two, without labor, but as a recreation, I could, if I wished, catch as many fish as I should want for two days, or earn enough money to support me a week.
A little hard-headed, Ripstone pippin-faced man, was conversing with a fat old gentleman in one corner; and two or three more old gentlemen, and two or three more old ladies, sat bolt upright and motionless on their chairs, staring very hard at Mr.
I don't know how master brought her to the house, being hard at work at the time.