سنن النسائي

It was narrated that An-Nu'man bin Bashir said: "I heard the Messenger of Allah (ﷺ) [SAW] say: 'That which is lawful is clear and that which is unlawful is clear, but between them there are matters which are doubtful.'" And sometimes he said: "But between them are matters that are not as clear. I will describe the likeness of that for you. Allah, the Mighty and Sublime, has a sanctuary and the sanctuary of Allah is that which He has forbidden. Whoever grazes around the sanctuary will soon transgress into the sanctuary. And whoever approaches a matter that is unclear, he will soon wind up in the sanctuary." And sometimes he said: "He will soon transgress, and indeed whoever mixes in doubt, he will soon cross into it."