How is the existence of a consensus on the obligation of hijab consistent with the scholars' disagreement regarding covering the face and hands? Is the aforementioned disagreement considered invalid, or is the principle of "blocking the means to evil" (sadd al-dhara'i') the point of contention? And is agreement preferable when there is fitna (temptation/strife)?

The consensus of the Ummah on the obligation of the principle of hijab is based on the texts of the Quran and Sunnah, and the practice of the Pious Predecessors. The disagreement among scholars is not concerning the principle of hijab itself, but rather in determining whether it includes the face and hands or not. This is a valid disagreement because the texts of revelation accommodate both interpretations. The wisdom behind this might be the flexibility of the religion and its suitability for every time and place. Some scholars may favor one of the two schools of thought given the circumstances of the people in their time. A permissible matter might also be prohibited to block the means to evil (sadd al-dhara'i'), as in His (Allah's) saying: "And do not insult those they invoke other than Allah, lest they insult Allah in enmity without knowledge."