In an unusual sense of the term "Aesop fable", one concerns a will. The fable is not attributed to Aesop, but he appears in it as a character. It is found in book IV of Phaedrus, who translated Aesop into Latin verse in the first century CE. I found it under the title “The Riddle of a Will” in the 1964 Penguin edition of Fables of Aesop, translated by S. A. Handford.

I adapted the story as a song called "Weaver of Wool". The riddle concerns the following bequest:
   What kind of lawyer would draft such a will?
   Father was not himself; father was ill.
   "Give to each child however well blessed
   One equal share that cannot be possessed."

You can find links to the music and lyrics here.