Sayyiduna Nu'man bin Bashir (may Allah be pleased with him) was saying on the pulpit: I heard the Messenger of Allah (peace and blessings be upon him) say: "The lawful is clear and the unlawful is clear, and between them are doubtful things. Whoever leaves the sin that is doubtful to him will all the more leave what is clear to him; and whoever ventures upon what he is in doubt about is close to falling into the unlawful. Indeed, every king has a protected pasture, and Allah's protected pasture on earth is the acts of disobedience to Him."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10817