Purity: Continuity and Drying of Moisture
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 282:
If there is a gap in between the acts of wuḍūʾ to the extent that the acts of wuḍūʾ cannot be commonly regarded as being performed in close succession, the wuḍūʾ is invalid. However, this does not apply if a legitimate excuse (ʿudhr) arises; for example, one forgets that he is performing wuḍūʾ, or the water runs out. In fact, when one wants to wash or wipe a place, if the moisture on all the places he has already washed or wiped has dried up, the wuḍūʾ is invalid. If only the moisture on the place that comes before the area he wants to wash or wipe has dried up – for example, when he wants to wash his left arm, the moisture on his right arm has dried up but his face is still wet – then his wuḍūʾ is valid.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)


