Allah, the Blessed and Exalted, says: "Those who follow the Messenger, the unlettered Prophet, whom they find written with them in the Torah and the Gospel, who commands them what is right and forbids them what is wrong, and makes lawful for them the good things and forbids them the impure things." [Surah al-A'raf: 157]
Imam al-Shafi'i (may Allah have mercy on him) said: "The good and the impure things are determined only by those who used to eat them, and they are the Arabs, who asked about this and concerning whom the rulings were revealed."
He (further) said: "I heard some of the people of knowledge say concerning the saying of Allah, the Mighty and Majestic: 'Say: I do not find, in what has been revealed to me, anything forbidden to one who would eat it' [Surah al-An'am: 145] that it means: of what you used to eat, except that it be carrion, and the things mentioned after it."
Imam al-Shafi'i (may Allah have mercy on him) said: "By inference from the Sunnah, this is the most fitting of its meanings."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / Q19353