An-Nu‘mān ibn Bashīr (may Allah be pleased with him) reported that he heard the Prophet (may Allah's peace and blessings be upon him) say: "Verily, the lawful is clear and the unlawful is clear, and between them are doubtful matters which many people do not know of. Whoever avoids doubtful matters clears his liability regarding his religion and his honor, and whoever falls into doubtful matters will fall into the unlawful, just like the shepherd who grazes his animals in the vicinity of a pasture declared prohibited (by the king) and is, thus, likely to let them graze in a prohibited area (and be punished for that). Verily, every king has a protected area and the protected area of Allah is His prohibitions. Verily, in the body there is a piece of flesh which if upright then the entire body will be upright, and if corrupt then the entire body will be corrupt. Verily, it is the heart."
عن النعمان بن بشير -رضي الله عنه- قال: سمعت النبي -صلى الله عليه وسلم- يقول: «إن الحلال بيِّن وإن الحرام بين، وبينهما أمور مُشْتَبِهَاتٌ لا يعلمهن كثير من الناس، فمن اتقى الشُّبُهات فقد اسْتَبْرَأ لدينه وعرضه، ومن وقع في الشبهات وقع في الحرام، كالراعي يرعى حول الحِمى يوشك أن يَرْتَع فيه، ألا وإن لكل مَلِك حِمى، ألا وإن حِمى الله محارمه، ألا وإن في الجسد مُضغة إذا صلحت صلح الجسد كله وإذا فسدت فسد الجسد كله ألا وهي القلب».
شرح الحديث :
The general rule is that everything that Allah and His Messenger made lawful and everything that they made unlawful is clear and evident. However, fear for the Muslim stems from doubtful matters. Whoever abandons those doubtful matters will keep his religion safe and intact by staying away from slipping into the unlawful. He will also protect his honor from people's slander caused by his committing such doubtful matters. Whoever does not avoid doubtful matters will expose himself either to falling into the unlawful or to people's backbiting and defamation. The Prophet (may Allah's peace and blessings be upon him) likened the one who commits the doubtful matters to a shepherd who grazes his camels or sheep near a private property, with the risk of having his animals graze inside that property for being so close. Similarly, the one who commits what is doubtful is getting too close to what is clearly unlawful, and is thus taking the risk of falling therein. The Prophet (may Allah's peace and blessings be upon him) referred to the fact that the external actions indicate whether the internal actions are righteous or corrupt. He clarified that the body contains a piece of flesh (the heart) which is responsible for the soundness of the whole body in case it is sound, and for its corruption in case it is corrupt.