Does the traveling person's wiping duration begin when they start wiping while residing, if they later travel before the resident period expires?
Chapter on Wiping over the Khuffayn (Leather Socks)
Al-Mughni
Book of Purification
Primary text
There are differing narrations from Imam Ahmad on this issue. One narration aligns with what al-Khiraqi mentioned, which is the view of al-Thawri, al-Shafi'i, and Ishaq (implying the resident ruling applies until the time runs out). Another narration states that they wipe the traveler's wiping period, provided the traveler's period has not expired, even if they wiped initially while resident for one or more prayers. This latter view is the Madhhab of Abu Hanifa, based on the Hadith, "The traveler wipes for three days and nights," because they traveled before the full duration expired, similar to one who travels before wiping after having the minor impurity.
Supporting text
The justification for the view favoring the resident ruling when wiping begins residentially is that the act of wiping is an act of worship that differs between residency and travel. Since one part of it (the beginning) occurred in residency, the ruling of residency prevails, similar to prayer. The Hadith implies that the traveler wipes for three days during their travel, applying to one who begins wiping during travel, and in this case, the time already spent residentially should be counted.