ccording to many Islamic scholars over the years, the story of Prophet Muhammad having a donkey and speaking to it is a false story. The story first appeared in The book "The Beginning and the End" written by Ibn Kathir, Chapter Six, Entry title: "The Conversation of the Donkey". The story goes like this:

"When Allah opened Khaybar to his prophet Muhammad – may Allah’s prayers and peace be upon him – he (Muhammad) received as his share of the spoils four sheep, four goats, ten pots of gold and silver and a black, haggard donkey.

The prophet – may Allah’s prayers and peace be upon him – ADDRESSED the donkey asking, ‘What is your name?’ THE DONKEY ANSWERED, ‘Yazid Ibn Shihab. Allah had brought forth from my ancestry 60 donkeys, none of whom were ridden on except by prophets. None of the descendants of my grandfather remain but me, and none of the prophets remain but you and I expected you to ride me. Before you, I belonged to a Jewish man, whom I caused to stumble and fall frequently so he used to kick my stomach and beat my back.’

The prophet – may Allah’s prayers and peace be upon him – said to him, ‘I will call you Ya’foor, Oh Ya’foor.’ Then Ya’foor REPLIED, ‘I obey.’ The prophet then asked, ‘Do you desire females?’ The donkey replied, ‘NO!’

So the prophet used to ride the donkey to complete his business and if the prophet dismounted from him he would send the donkey to the house of the person he wanted to visit and Ya’foor would knock at the door with his head. When the owner of the house would answer the door, the donkey would signal to that person to go see the prophet.
When the prophet died, the donkey went to a well belonging to Abu Al-Haytham Ibn Al-Tahyan and threw himself in the well out of sadness for the prophet’s death, making it his grave."