Bg 18.41

brahmana-ksatriya-visam
sudranam ca paran-tapa
karmani pravibhaktani
svabhava-prabhavair gunaih

Word for word: 
brahmana — of the brahmanas; ksatriya — the ksatriyas; visam — and the vaisyas; sudranam — of the sudras; ca — and; param-tapa — O subduer of the enemies; karmani — the activities; pravibhaktani — are divided; svabhava — their own nature; prabhavaih — born of; gunaih — by the modes of material nature.

Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Brahmanas, ksatriyas, vaisyas and sudras are distinguished by the qualities born of their own natures in accordance with the material modes, O chastiser of the enemy.