It is narrated from Sayyidah Aishah (may Allah be pleased with her): "Impurity does not come upon water." (b) Imam al-Shafi'i (may Allah have mercy on him) says that our position is what we narrate from Zayd bin Thabit (may Allah be pleased with him) and al-Qasim bin Muhammad (may Allah have mercy on him), that they ordered a man to take the ritual bath (ghusl) for major impurity in a well, and something similar in meaning is narrated from Sayyiduna Umar (may Allah be pleased with him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 1269