Sayyiduna Abu Hurairah (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: "A mortgaged animal may be ridden in exchange for its maintenance, and similarly, a milking animal when mortgaged, its milk may be drunk in exchange for its maintenance. And whoever drinks its milk or rides it, he must bear its expenses."
Hadith Referenceالمنتقى ابن الجارود / كتاب البيوع والتجارات / 665