From Sahih Muslim (Hadith 2295):
Umm Salama, the wife of Allah's Apostle (ﷺ), said I used to hear from people making a mention of the Cistern, but I did not hear about it from Allah's Messenger (ﷺ). One day while a girl was combing me I heard Allah's Messenger (ﷺ) say:
Reference: Muslim 2295