حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، أَنْبَأَنَا حَمَّادُ بْنُ زَيْدٍ، عَنْ مُجَالِدٍ، عَنِ الشَّعْبِيِّ، عَنِ النُّعْمَانِ بْنِ بَشِيرٍ، قَالَ سَمِعْتُ رَسُولَ اللَّهُ صلى الله عليه وسلم يَقُولُ ‏"‏ الْحَلاَلُ بَيِّنٌ وَالْحَرَامُ بَيِّنٌ وَبَيْنَ ذَلِكَ أُمُورٌ مُشْتَبِهَاتٌ لاَ يَدْرِي كَثِيرٌ مِنَ النَّاسِ أَمِنَ الْحَلاَلِ هِيَ أَمْ مِنَ الْحَرَامِ فَمَنْ تَرَكَهَا اسْتِبْرَاءً لِدِينِهِ وَعِرْضِهِ فَقَدْ سَلِمَ وَمَنْ وَاقَعَ شَيْئًا مِنْهَا يُوشِكُ أَنْ يُوَاقِعَ الْحَرَامَ كَمَا أَنَّهُ مَنْ يَرْعَى حَوْلَ الْحِمَى يُوشِكُ أَنْ يُوَاقِعَهُ أَلاَ وَإِنَّ لِكُلِّ مَلِكٍ حِمًى أَلاَ وَإِنَّ حِمَى اللَّهِ مَحَارِمُهُ ‏"‏ ‏.‏

An-Numan bin Bashir narrated that the Messenger of Allah (S) said: "The lawful is clear and the unlawful is clear, and between that are matters that are doubtful (not clear); many of the people do not know whether it is lawful or unlawful. So whoever leaves it to protect his religion and his honor, then he will be safe, and whoever falls into something from them, then he soon will have fallen into the unlawful. Just like if someone grazes (his animals) around a sanctuary, he would soon wind up in it. Indeed for every king is a sanctuary (pasture), and indeed Allah's sanctuary is what He made unlawful." Translation Not Available

Book reference: Jamiya Tirmidhi Book 14 Hadith 1205
Web reference: Jamiya Tirmidhi Volume 3 Book 12 Hadith 1205