Sahih Al Bukhari – Book of Sales And Trade

Volumn 003, Book 034, Hadith Number 286.
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Narated By Al-Miqdam

Razi Allah Anhu

: The Prophet 

Peace Be Upon Him

 said, "Nobody has ever eaten a better meal than that which one has earned by working with one's own hands. The Prophet of Allah SWT, David

Alaihi Salam

 used to eat from the earnings of his manual labor."