It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with him) that one of the wives of the Prophet (peace and blessings be upon him) bathed in a tub. He (peace and blessings be upon him) came to perform ablution or bathe from it, and she said: O Messenger of Allah! I was in a state of major ritual impurity. He (peace and blessings be upon him) said: "Water does not become impure."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 902