If a person leaves the prayer upon finding water to perform purification, must they restart the prayer?
Chapter on Tayammum
Al-Mughni
Book of Purification
Primary text
If the person exits the prayer to perform Wudu after finding water, they are obligated to restart the prayer anew. This is because purification is a prerequisite for prayer, and it has been nullified by the invalidation of the Tayammum, meaning the prayer cannot continue without its prerequisite. Moreover, one cannot continue a past portion of the prayer while having left it before completion.
Supporting text
A secondary opinion suggests that the prayer completed prior to the discovery of water might be built upon, similar to cases where minor impurity occurs during prayer. However, the sound position rejects this building upon the past, arguing that the prior portion was based on a weak purification (Tayammum), unlike the case where a minor impurity occurs unexpectedly.