A hardworking child does not lack one to wash him.
Comment
In the original proverb, hardwork is a prerequisite to being washed, hence encouraging. In the postproverbial, being dirty is stressed as the outcome of hard work.
Postproverbials
Postproverbial: Mwana ũrĩ kĩo ndagaga, gĩko. Translation: A hardworking child does not fail to be dirty.