Musannaf Ibn Abi Shayba 18:994

Abu Bakr narrated to us, he said: 'Abdah bin Sulayman narrated to us, from Sa'id, from Abu Ma'shar, from Ibrahim, he said: "If he entered with their permission and it (the animal) wounded him, they are liable. And if he entered without their permission and it wounded him, they are not liable."