Numan bin Bashir reported,

I heard the Messenger of Allah ﷺ say, "The lawful is clear and the unlawful is clear, and between them are doubtful matters which many people do not know. Whoever avoids the doubtful matters protects his religion and his honor, but whoever falls into the doubtful matters is like a shepherd grazing his flock around a private pasture, on the verge of letting them stray into it. Indeed, every king has a sanctuary, and Allah's sanctuary on His earth is what He has forbidden. Indeed, in the body there is a piece of flesh which, if sound, the whole body is sound, and if corrupt, the whole body is corrupt. Indeed, it is the heart."

Bukhari 52

Sahih

حدثنا أبو نعيم حدثنا زكرياء عن عامر قال سمعت

النعمان بن بشير يقول

سمعت رسول الله ﷺ يقول الحلال بين والحرام بين وبينهما مشبهات لا يعلمها كثير من الناس فمن اتقى المشبهات استبرأ لدينه وعرضه ومن وقع في الشبهات كراع يرعى حول الحمى يوشك أن يواقعه ألا وإن لكل ملك حمى ألا إن حمى الله في أرضه محارمه ألا وإن في الجسد مضغة إذا صلحت صلح الجسد كله وإذا فسدت فسد الجسد كله ألا وهي القلب

البخاري 52صحيح
Contents
Reference
Commentary
Ayat
Collection
Sahih Bukhari
Book
Faith
Chapter
Virtue of one who seeks to protect his religion
Numbering
Darussalam 52
Bukhari 52