"Rub-A-Dub-Dub" is an English language nursery rhyme first published at the end of the eighteenth century.**(citation needed - the 1798 publication is not listed in the Roud Folk Song Index) It has a Roud Folk Song Index number of 3101.
Three men in a tub,
And who do you think they were?
The butcher, the baker,
They all sailed out to sea,
'Twas enough to make a man stare