The first is that it runs contrary to the textual evidence; and an analogy that conflicts with a text is termed, in the terminology of the legal theorists, an invalid analogy.
The second is that it is an analogy despite a relevant difference. The differences are several: …
The first difference is that purification by tayammum is confined to two limbs, whereas purification with water in wudu involves four limbs, and in ghusl the entire body.
The second difference is that the two forms of purification differ in the case of purification with water, whereas purification by tayammum does not differ.
The third difference is that purification with water involves physical cleansing, as well as spiritual purification, whereas tayammum involves no cleansing.
- The hands in the ruling on tayammum are mentioned in unqualified terms, so they are to be understood in light of the qualified wording in the verse on wudu. This was answered by stating that an unqualified expression is only understood in light of a qualified one when they share the same ruling. Where their rulings differ, the unqualified expression is not understood in light of the qualified one.
The same applies to sequence and continuity in the case of minor ritual impurity.
His statement, “The same applies to sequence and continuity in the case of minor ritual impurity,” means that among the obligatory elements of tayammum for minor ritual impurity are sequence and continuity.
Sequence means beginning with the face before the hands.
Its evidence is Allah’s saying, Exalted is He: “Wipe your faces and your hands” [Quran 5:6]. He mentioned the face before the hands. The Prophet, peace and blessings be upon him, said: “Begin with that which Allah began with.” (1)