Amr bin Dinar says: I said to Jabir bin Zayd (may Allah have mercy on him): They claim that the Messenger of Allah (peace and blessings be upon him) "forbade eating the meat of domestic donkeys at the time of Khaybar." He said: Al-Hakam bin Amr (may Allah be pleased with him) used to say the same from the Messenger of Allah (peace and blessings be upon him), but Ibn Abbas (may Allah be pleased with them both) rejected that and recited this verse: "Say: I do not find, in what has been revealed to me, anything forbidden" [Surah al-An'am: 145]. The people of the pre-Islamic era of ignorance (Jahiliyyah) used to abandon certain things out of disgust, so Allah, Lord of Might, made the lawful and the unlawful completely clear. What Allah has made lawful is lawful, what He has made unlawful is unlawful, and what has been passed over in silence is pardoned. Then he recited this verse: "Say: I do not find, in what has been revealed to me, anything forbidden to one who would eat it, unless it be carrion, or blood poured forth, or the flesh of swine" [Surah al-An'am: 145].
Had Abdullah bin Abbas (may Allah be pleased with them both) known that the Prophet (peace and blessings be upon him) had declared it definitively unlawful, he would not have turned to anything else; but he did not know it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19459