Green’s Dictionary of Slang

(US) be quiet! shut up!

1935		R. Chandler ‘Nevada Gas’ in Spanish Blood (1946) 142: ‘Where we going, punk?’ De Ruse asked casually. ‘Save it,’ Chuck snarled.
1947		B. Schulberg Harder They Fall (1971) 17: ‘Save it, Eddie’ she said.
1953		J. Thompson Alcoholics (1993) 8: Save it! Why didn’t you call me?
1963		‘Nino Culotta’ Gone Fishin’ 164: ‘There was no need for you to bring beer. We have some.’ ‘Save it, mate,’ Dennis said. ‘Yer out o’ work, yer know.’.
1993		K. Scott Monster (1994) 107: Oh shit, I thought, here comes one of those sermons [...] Save it, lady.
2003		McGill Reed Dict. of N.Z. Sl.
2021		P. Papathanasiou Stoning 156: Joe interrupted Manolis’s questioning. ‘Look, Dick Tracy, save it. I know why I’m here’.