воду в ступе толочь - вода и будет

Set phrase: beating the air is just beating the air, it's no use beating the air, it's no use fishing in the air, it's no use ploughing the air, it's no use thrashing over old straw, it's no use whistling jigs to a milestone, whether you boil snow or pound it, you can have but water of it (useless and senseless work always results in nothing)