The question of purity and impurity of things has always occupied the thought of Muslim jurists due to the consequential permissibility or impermissibility of the use or consumption of many things. Juristic opinions in this regard vary and giving preponderance to one position over the other needs subtle understanding and comprehensive analysis.
Dr. Rajab Abu Maleeh, Ph. D. in Shari`ah stated:
The issue of the transformation of impurity is an old one that had been addressed by a number of earlier jurists. However, this issue has resurfaced in the last years following the Muslims’ mingling with non-Muslims in Europe, America and other non-Muslim countries. This also has followed the progress in science which resulted in making pig fats an essential ingredient in many things that are used by the Muslims, starting with sweets, through detergents, cosmetics and the like, to vaccines that provide man with immunity against diseases, such as infantile paralysis and the likes. Besides, the pig is impure according to the unanimous agreement of Muslim jurists, and in turn people suppose that if any part of it is added to anything pure, it transforms it into an impure substance.
Here comes the role of the Fatwa in this open world as a means of employing the earlier legacy of Fiqh and benefiting from it in removing restriction and harm for a no small number of Muslims living in non-Muslim western and eastern countries.
Hence, the Fatwa on this issue – in brief – is that when impurity, whether a pig or any other form, transforms into another substance through chemical treatment, it thus turns into something else that is not impure, as is the case when wine transforms into vinegar. Likewise, sewage (liquid) that is chemically treated and frequently refined until it returns pure water, free of all impurities, becomes pure water that is edible and suitable to be used in ablution, washing and the like.
Though the issue is an old one, modern applications turned it into a new one that is classified under the category of occurrences that require contemporary Ijtihad.
Such an issue was tackled by his eminence, scholar Dr. Yusuf al-Qaradawi in his book Fiqh of Taharah [Jurisprudence of Purification], in which he quoted the sayings propounded in the several juristic schools [Madhahib] on the issue:
It is stated in the Hanafi book Al-Bahr Al-Ra’iq [The Calm Sea] that “Among the matters through which purification takes place is the change of the substance … even if it is in another substance, such as pork and dead (animal) meat that falls in the saltcellar and thus turns into salt; it then becomes edible. Likewise, animal and human excrement, when it burns and thus turns into ashes, becomes pure, according to Muhammad (an eminent disciple of Abu Hanifah).
Moreover, the Hanafi scholars agreed to the purity of wine in case it transforms into vinegar, whether it transforms by itself or through mixture with other substances.
However, the Maliki position that is adopted in issuing Fatwas is like the Hanafi one on this issue, meaning the one they – Hanafis – follow in issuing Fatwas, including the opinion of Muhammad and what was reported from Abu Hanifah too.
The same opinion is adopted in the Zhahiri position, being represented by Abu Muhammad ibn Hazm, who said well-grounded words in Al-Muhalla supporting the opinion that the ruling changes upon the change and transformation of the substance.
Similarly, the Zaydi position, as stated in Al-Azhar (a Zaydi book of fiqh) and their other references, as well as the Imamiyyah position, assume the same opinion.
Moreover, the strictest position that denies the purity of substance upon transformation is the Shafi`i one, where scholars keep attaching the ruling on impurity and the prohibition to the substance even if it changes and transforms into another substance with another name and another description, with the exception of wine when it transforms by itself, without interference or treatment by man, and the skin of dead animal when it is tanned. The same opinion is adopted by Abu Yusuf – the Hanafi scholar – and is one of the opinions in the Maliki madh-hab. Their argument in distinguishing wine from other substances is that it transforms from something pure, namely grapes and the like, and thus when it transforms into vinegar, it merely returns to its original form and thus turns pure.
However, they are quite mistaken in such argument, since all impure substances are transformed from pure substances. For, we have indicated that Almighty Allah – Exalted be He – has created all things pure. That is why urine and excrement – being unanimously viewed as impure – transform from the two pure substances of food and drink. This is the famous opinion reported in the Hanbali madh-hab too.