It was narrated from 'Abdullah bin 'Umar that the Messenger of Allah (ﷺ) stood up and said:
"No one of you should milk from the livestock of another man without his permission. Would anyone of you like someone to break into his storeroom and take his food? The udders of their livestock store food for them, so none of you should milk the livestock of another man without his permission."
English reference: Vol. 3, Book 12, Hadith 2302
Arabic reference: Book 12, Hadith 2390