Sayyiduna Zayd bin Khalid al-Juhani (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) said: "Whoever keeps a stray animal with himself is himself astray, as long as he does not announce it."
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 5262