Answered by Shaykh Amjad Rasheed
An ill man needs to apply an adhesive patch to his skin. The patch contains medicines dissolved in synthetic ethanol (aka. ethyl alcohol). It is not possible for him to remove the patch for every prayer because this would harm him greatly. How can this man pray?
Applying the Patch
If he knows that this adhesive contains filth, the normal ruling is that it is prohibited for him to apply it [m: to his skin, etc.] unless there is a need, like medical treatment. However, this [m: exception] has two conditions: that he know personally (even if he is morally corrupt) or through the statement of an upright Muslim doctor that this [m: patch] will benefit him, and that the impure medicine be specifically required, in that no pure medicine could take its place (Tuhfa, 9.170; others). In this case, it would be permissible for him to use [m: the patch].
Praying with the Patch
If it is possible for him to remove [m: the patch] and purify the affected area in order to pray, then it is obligatory for him to do so. If it isn’t possible for him to do this, such as if he fears, for example, an increase in his illness or a delay in recovery, then he prays with it and later repeats the prayer due to the [m: invalidity caused by the] presence of filth [m: during the first prayer]. This is the ruling in our school.
It is valid to follow what the Hanafis have said [m: regarding the purity of synthetic alcohol], if taken from a scholar of their school, while observing the rulings of prayer in our school. [m: This is] based on the position of the erudite scholar Ibn Ziyad which states that the prohibited mixing [m: of schools of thought] is what pertains to a single issue. The rulings of the pure and impure and the rulings of prayer are two issues, not a single issue, so [m: following two different schools of thought in these matters] does not constitute prohibited mixing according to him. And Allah knows best.