Islamic jurisprudence specifies which foods are ( "lawful") and which are ( "unlawful"). This is derived from commandments found in the Qur'an, the holy book of Islam, as well as the Hadith and Sunnah, libraries cataloging things the Islamic prophet Muhammad is reported to have said and done. Extensions of these rulings are issued, as fatwas, by mujtahids, with varying degrees of strictness, but they are not always widely held to be authoritative. According to the Quran, the only foods explicitly forbidden are meat from animals that die of themselves, blood, the meat of swine (porcine animals, pigs), and animals dedicated to other than Allah (either undedicated or dedicated to idols), but a person is not guilty of sin in a situation where the lack of any alternative creates an undesired necessity to consume that which is otherwise unlawful. (Quran 2:173) This is the "law of necessity" in Islamic jurisprudence: "That which is necessary makes the forbidden permissible", which, in the case of dietary laws, allows one to eat pork or carrion, or drink wine or ethanol if one were starving or dying of thirst (although the Shafi'i madhhab differs on the issue of ethanolic drinks).