空口無憑

mere verbal statement cannot be taken as proof (idiom)

empty / air / sky / in vain

to empty / vacant / unoccupied / space / leisure / free time

incomplete meal of a single dish / meat or vegetable dish without rice or wine / rice without meat or vegetables

mouth / classifier for things with mouths (people, domestic animals, cannons, wells etc) / classifier for bites or mouthfuls

not to have / no / none / not / to lack / un- / -less

to lean against / to rely on / on the basis of / no matter (how, what etc) / proof