Abu Dawud Book 8, Hadith Number 2613.

Narated By Samurah ibn Jundub : The Prophet (PBUH) said: When one of you comes to the cattle, he should seek permission of their master if he is there; if he permits, he should milk (the animals) and drink. If he is not there, he should call three times. If he responds, he should seek his permission; otherwise, he may milk (the animals) and drink, but should not carry (with him).