Abu Dawud Book 18, Hadith Number 3620.

Narated By Awf ibn Malik : The Holy Prophet (PBUH) gave a decision between two men, and the one against whom the decision was given turned away and said: For me Allah sufficeth, and He is the best dispenser of affairs. The Holy Prophet (PBUH) said: Allah, Most High, blames for falling short, but apply intelligence, and when the matter gets the better of you, say; For me Allah sufficeth, and He is the best disposer of affairs.