Sayyidina Nu’man ibn Bashir (RA) reported that he heard Allah’s Messenger (SAW) say, “The lawful is clearly defined and the unlawful is clearly defined, but between them are matters that are doubtful. Many of the people cannot decide whether they are lawful or unlawful. So, he who avoids them to guard his religion and honour has indeed, taken the safe path. And he who falls into some of it nearly falls into the unlawful, just as a shepherd who grazes his animals on the borders of a sanctuary might take them to the other side. Know that every king has a sanctuary. And know that the sanctuary of Allah is that which he has declared unlawful.
[Ahmed 18375, Bukhari 52, Muslim 1599, Abu Dawud 3329, Nisai 4463, Ibn e Majah 3986]