Qitzur Shulchan Arukh – 182:13
It is prohited to get benefit from anything of a friend’s without his knowledge. Even if it is certain to him that when the owners would be informed, they would be happy and rejoice because of their love for him. In any case, it is prohibited.
Therefore, someone who enters his friend’s orchard or garden, he is not allowed to pick fruit without the knowledge of the owners. Even if the owner of the orchard and the owner of the garden love him and is his friend [as close] as his own soul, and would certainly be happy and rejoice when he is informed that this one benefited from his fruit, in any case since now he does not know about this, he is getting benefit in a prohibited manner.
We must warn the masses about this, who stumble in this because of lack of knowledge.