Maliks Muwatta Book 007, Hadith Number 005A.

Section : Concerning Prayer in the Night.

Yahya related to me from Malik from Ismail from Ibn Abi Hakim that he had heard that the Messenger of Allah, may Allah bless him and grant him peace, heard a woman praying at night. He said, "Who is that?" and someone said to him, "It is al-Hawla bint Tuwayt, she does not sleep in the night." The Messenger of Allah, may Allah bless him and grant him peace, disapproved of that and his disapproval showed in his face. Then he said, "Allah, the Blessed and Exalted, does not become weary, but you become weary. Take on whatever is within your capability."