Is the purity of the sutrah a condition for the validity of the prayer?

Question:
The author’s deduction regarding the purity of the sutrah in prayer?

Answer:
From the hadith of Asma’, he said to her: “Then pray in it; wash it, then pray in it.” This indicates that one should not pray in it as long as there is ritual impurity in it. It is necessary for the sutrah to be pure, as well as the body; all of it. It is necessary for the purity of the three: the body, the place, and the garments in which one prays. It is necessary for the purity of all of them. His saying, (Exalted and Majestic is He): [Al-Muddaththir: 4], this encompasses all of that.
Q: Is the sutrah not a place or a garment?
A: The sutrah that she wears; what is the sutrah that is in front? His intention is the clothing, meaning this is his intention: the sutrah with which the woman covers herself.
As for the sutrah that is in front of him, it is not a condition that it be pure. The important thing is that what she covers her ‘awrah with must be pure, just as the man’s garments must be pure, exactly the same.