Sahih Muslim
The Book of Prayers (Kitab Al-Salat)
Book Number: 004 / Hadith Number: 1717
'A'isha said: The Messenger of Allah (way peace be upon him) came to me when a woman was sitting with me. He said: Who is she? I said: She is a woman who does not sleep but prays. He said: Do such acts which you are capable of doing. By Allah, Allah does not grow weary but you will grow weary. The religious act most pleasing to Him is one the doer of which does it continuously. (And in the hadith transmitted by Abu Usama [the words are]:" She was a woman from Banu Asad." )