at\ it

at\ it
adj. phr.
Busily doing something; active.

His rule for success was to keep always at it.

The couple who owned the little cleaning shop were at it early and late.

Mr. Curtis heard a loud crash in the next apartment - the neighbors were at it again.

Словарь американских идиом. — СПб., Изд-во "Лань". . 1997.