Majma al-Zawaid — Hadith 18113

Sayyiduna Ammar bin Yasir (may Allah be pleased with him) reports this saying of the Prophet (peace and blessings be upon him): "Indeed, the lawful is clear and the unlawful is clear, and between the two are some doubtful matters. Whoever guards himself against them, they will be a protection for his religion; and whoever falls into them may soon fall into the major sins too, like one who grazes around a protected pasture who may well enter the pasture itself. And every king has his own protected pasture."
Abu Ya'la recorded it; its chain contains a narrator, Musa bin Ubaydah, who is matruk (abandoned).