This narration can be understood to mean that if the person drinking was thought to be a Jew but there was no certainty of it, then one should not assume impurity unless it is definitively established. Alternatively, it could refer to a person who was previously a Jew but later accepted Islam. However, if the person is confirmed to be a Jew at the time of drinking, it is not permissible to perform Wudu' with their leftover water, as previously explained. The Shaykh (Al-Mufid), may Allah سبحانه وتعالى support him, then said: "It is not permissible to purify oneself with the leftover water of a dog or a pig. If a dog licks a vessel, the water inside must be discarded, and the vessel must be washed three times - twice with water and once with soil, with the soil being used in the middle wash. Then the vessel must be dried and can be used." This is supported by clear evidence.
Commentary #11