It is narrated from Sayyiduna al-Miqdam bin Ma'dikarib (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "No one has eaten any food better than eating from the earnings of his own hands, and Dawud (peace be upon him) used to eat only from the earnings of his own hands."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 17765