Narrated Al-Nu'man b. Bashir:
I heard the Messenger of Allah ﷺ say: What is lawful is clear and what is unlawful is clear, but between them are certain doubtful things. I give you an example for this. Allah has a preserve, and Allah's preserve is the things He has declared unlawful. He who pastures (his animals) round the preserve will soon fall into it. He who falls into doubtful things will soon be courageous.

حَدَّثَنَا أَحْمَدُ بْنُ يُونُسَ، قَالَ حَدَّثَنَا أَبُو شِهَابٍ، حَدَّثَنَا ابْنُ عَوْنٍ، عَنِ الشَّعْبِيِّ، قَالَ سَمِعْتُ النُّعْمَانَ بْنَ بَشِيرٍ، - وَلاَ أَسْمَعُ أَحَدًا بَعْدَهُ يَقُولُ - سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ " إِنَّ الْحَلاَلَ بَيِّنٌ وَإِنَّ الْحَرَامَ بَيِّنٌ وَبَيْنَهُمَا أُمُورٌ مُشْتَبِهَاتٌ " . وَأَحْيَانًا يَقُولُ " مُشْتَبِهَةٌ " . " وَسَأَضْرِبُ لَكُمْ فِي ذَلِكَ مَثَلاً إِنَّ اللَّهَ حَمَى حِمًى وَإِنَّ حِمَى اللَّهِ مَا حَرَّمَ وَإِنَّهُ مَنْ يَرْعَ حَوْلَ الْحِمَى يُوشِكْ أَنْ يُخَالِطَهُ وَإِنَّهُ مَنْ يُخَالِطِ الرِّيبَةَ يُوشِكْ أَنْ يَجْسُرَ " .