Sunan Abi Dawud Book 15, Hadith 88
Jabir reported the Prophet (ﷺ) as saying when an ass which had been branded on its face passed him. Did it not reach you that I cursed him who branded the animals on their faces or struck them on their faces. So he prohibited it.
Anas bin Malik said “I brought my brother when he was born to Prophet(ﷺ) to chew something for him and rub his palate with it and found him in a sheep pen branding the sheep, I think, on their ears.”
The Messenger of Allah (ﷺ) was present with a she-mule which he rode, so Ali said: If we made asses cover mares we would have animals of this type. The Messenger of Allah (ﷺ) said: Only those who do not know do that.