Another issue of great importance is the mixing of something lawful with something inherently unlawful, such as impurities mixing with water or other liquids. The scholars of Kufa prohibit any water or liquid into which an impurity falls, whether its quantity is small or large. They then judge that impurity cannot reach beyond the point to which movement in the water extends, setting the measure at ten cubits by ten cubits.

Some of them say that if an impurity falls into a well, it cannot be purified; rather, it must be filled in. Some of their jurists say that either a specified number of bucketfuls must be drawn from it, or all its water must be drawn out, according to their well-known rules. This follows from their view that water and other liquids become impure when an impurity falls into them.

The scholars of Medina take the opposite position: according to them, water does not become impure unless it undergoes a change. They do, however, hold two views on whether a small quantity of water becomes impure through a small amount of impurity. Ahmad’s position is close to this, as is al-Shāfi‘ī’s, although these two, unlike Mālik, define a small quantity as less than two qullahs (large jarfuls). Conflicting views are reported from Mālik concerning foods; likewise, within Ahmad’s school there is disagreement concerning liquids other than water.

It is clear that this position accords more closely with the Book and the Sunnah. The designation “water” still applies, and the designation on account of which it was lawful before the impurity fell into it remains unchanged. The Sunnah of the Messenger of Allah—may Allah bless him and grant him peace—concerning the well of Budā‘ah and other cases indicates that it does not become impure. Nor is this contradicted by the hadith prohibiting urination in stagnant water, for it does not explicitly address the point at issue: the ruling may apply specifically to urine.