Riyad as-Salihin (The Meadows of the Righteous)
by Imam Nawawi
209. Chapter: The recommendation to pray two rak'ats after doing wudu'
1146. Abu Hurayra reported that the Messenger of Allah, may Allah bless him and grant him peace, said to Bilal, "Bilal, tell me that action that you have done since entering Islam which gives you the most reason to hope for I heard the sound of your sandals ahead of me in the Garden." He said, "I have done no action which gives me more reason to hope than that of never purifying myself at any time of the night or day without then praying after that purification as much as is written for me to pray." [Agreed upon]