Sunan Ibn Majah Book 1, Hadith 117
The Prophet and she used to perform ablution together for prayer.
"Often my hand would touch the hand of the Messenger of Allah while performing ablution from a single vessel." (Hasan)
Abu `Abdullah bin Majah said: "I heard Muhammad say: 'Umm Subyah was Khawlah bint Qais. I mentioned that to Abu Zur`ah and he said: "It is true."
On the night of the jinn, the Messenger of Allah said to him: "Do you have water for ablution?" He said: "No, I have nothing, but some Nabidh in a vessel." He said: "Good dates and pure water (i.e. there is no harm from the mixing of the two)." So he performed ablution with it. This is the narration of Waki'.