Green’s Dictionary of Slang

(drugs) hashish; occas. in sing.

1977		L. Young et al. Recreational Drugs.
1980		‘Gloss. of Drug Terms’ National Instit. Drug Abuse.
1995		G. Cuomo Couple of Cops 158: We occasionally ran into hash, peddled in what was called a sole, because it was shaped like a foot. A sole weighed about half a pound. Users would shave the hash with a razor and smoke it in a pipe.
2001		ONDCP Street Terms 20: Soles — Hashish.