This fable tells us the story of a man who wanted to buy a donkey. I narrated this fable and you can find it by clicking the link The Donkey & His Purchaser.
The man asks to take the donkey on trial before he buys him and so he does.
But as soon as he takes him to his stable and sees that the donkey went and chose a place next to the laziest and greediest beast in it, he takes him back to the market.
The seller is surprised to see him back so soon and wonders how the purchaser could have decided so soon if he likes the donkey or not. To that the man replies “I could see what sort of beast he is from the companion he chose for himself".
The moral lesson of the story is that "A man is known by the company he keeps".
In other words, a person is considered similar to the people whose companionship he enjoys. In the story the donkey chose the company of an idle and voracious animal and that reveals his character in the eyes of his purchaser and indicates the the course of action that should be adopted towards him, which in this case is to return the donkey to his owner.