“Allah has forbidden the sale of wine, carrion, swine, and idols.” They said, “What about the fat of carrion? Ships are caulked with it, hides are treated with it, and people use it for lamps.” He said, “No; it is unlawful.” (1) That is, its sale is unlawful, even though they mentioned that people benefit from it. Is it permissible to benefit from it? The answer is yes: it may be used in a manner that does not spread its impurity—for example, hides may be treated with it, ships may be caulked with it, and people may use it for lamps.

His statement, “nor oils contaminated with impurity,” means that the sale of contaminated oils is likewise invalid. These are oils that were originally pure but have been affected by impurity—for example, a person has a gallon of oil into which some impurity falls. According to the established school of law, contaminated oils may not be sold because they cannot be purified; and if they cannot be purified, they become like intrinsically impure oils. The correct view, however, is that the sale of contaminated oils is permissible, because they can be purified. Thus, they are like the sale of a garment contaminated with impurity.

Accordingly, the author is correct in stating that intrinsically impure oils may not be sold, and his evidence is the hadith of Jabir, may Allah be pleased with him: “Allah has forbidden the sale of wine …” As for contaminated oils, the author holds that they may not be sold. The correct view is that their sale is permissible, because the prohibition of their sale is based on the assumption that they cannot be purified. Yet the correct view is that they can be purified. But how can they be purified when they are oils?

The answer is that this may be done by adding substances that purify them, or by adding water to them and boiling them. In short, whenever they can be purified, their sale is permissible.