The earliest known illustration of a counterweight trebuchet comes from a 1187 commentary on Saladin's own conquests, but the source itself states there is little to no consensus as to where and when the counterweight trebuchet was first developed.
What would resolve this Additional dated illustrations, textual descriptions, or archaeological finds from the tenth to twelfth century Islamic or Byzantine world that predate or corroborate the 1187 illustration.
OpenHistory of siege technologyWikipedia: Trebuchet