Manusmriti
एकमेव तु शूद्रस्य प्रभुः कर्म समादिशत् । एतेषामेव वर्णानां शुश्रूषामनसूयया ॥ ९१ ॥
One occupation only the lord prescribed to the Sudra, to serve meekly even these (other) three castes.
english translation
ekameva tu zUdrasya prabhuH karma samAdizat । eteSAmeva varNAnAM zuzrUSAmanasUyayA ॥ 91 ॥
hk transliteration by Sanscript