Sahih Muslim Book 009, Hadith Number 3510.
Chapter: Ila and keeping away from wives.
Ibn Abbas (Allah be pleased with them) is reported to have said: I intended to ask Umar about those two ladies who had pressed for (worldly riches) during the lifetime of the Holy Prophet (may peace be upon him), and I kept waiting for one year, but found no suitable opportunity with him until I happened to accompany him to Mecca. And as he reached Marr al Zahran he went away to answer the call of nature, and he said (to me): Bring me a jug of water, and I took that to him. After having answered the call of nature, as he came back, I began to pour water (over his hands and feet), and I remembered (this event of separation of Allah's Apostle [may peace be upon him] from his wives). So I said to him: Commander of the Faithful, who are the two ladies (who had pressed the Holy Prophet [may peace be upon him] for providing comforts of life) and I had not yet finished my talk when he said: They were 'Aisha and Hafsa.