Sahih Muslim
The Book of Prayers (Kitab Al-Salat)
Book Number: 004 / Hadith Number: 1716
'Urwa b. Zubair reported that 'A'isha, the wife of the Apostle of Allah (may peace be upon him), told him that (once) Haula' dint Tuwait b. Habib b. Asad b. 'Abd al-'Uzzi passed by her (at the time) when the Messenger of Allah (may peace be upon him) was with her. I ('A'Isha) said: It Is Haula' bint Tuwait and they say that she does not sleep at night. Upon this the Messenger of Allah (may peace be upon him) said: (Oh) she does not sleep at night! Choose an act which you are capable of doing (continuously). By Allah, Allah would not grow weary, but you will grow weary.