Abu Dawud Book 2, Hadith Number 1284.
Chapter : Prayer in the forenoon.
Narated By Nu’aym ibn Hammar : I heard the Apostle of Allah (PBUH) say: Allah, the Exalted, says: Son of Adam, do not be helpless in performing four rak’ahs for Me at the beginning of the day: I will supply what you need till the end of it.