Hand Over Fist
(idiomatic) Quickly or in great quantity, especially in reference to earning money.
Example: He didn't earn much, but the company seemed to rake in money hand over fist.
1880, Robert Louis Stevenson, Letters vol. I, chapter 4
Are you coming over again to see me some day soon? I keep returning, and now hand over fist, from the realms of Hades: I saw that gentleman between the eyes, and fear him less after each visit.
1888, Rolf Boldrewood, Robbery Under Arms, chapter 39
Now, since cattle had risen and meat and all to such a price, he was making money hand over fist.