وَمَنْ ابْتَدَأَ الْمَسْحَ وَهُوَ مُقِيمٌ، فَسَافَرَ قَبْلَ تَمَامِ يَوْمٍ وَلَيْلَةٍ: مَسَحَ تَمَامَ ثَلَاثَةِ أَيَّامٍ وَلَيَالِيَهَا.
Meaning: If a person begins wiping while resident, then starts travelling before completing a day and a night, the person may wipe for the full three days and nights.
The 72 hours are measured from the original start of the wiping period, not as a fresh 72-hour allowance starting at departure.
If the resident allowance has already expired, embarking on a journey does not revive a concession that ended.