Bg 18.41

brāhmaṇa-kṣatriya-viśāṁ
śūdrāṇāṁ ca paran-tapa
karmāṇi pravibhaktāni
svabhāva-prabhavair guṇaiḥ
Synonyms: 
brāhmaṇa — of the brāhmaṇas; kṣatriya — the kṣatriyas; viśām — and the vaiśyas; śūdrāṇām — of the śūdras; ca — and; param-tapa — O subduer of the enemies; karmāṇi — the activities; pravibhaktāni — are divided; svabhāva — their own nature; prabhavaiḥ — born of; guṇaiḥ — by the modes of material nature.
Translation: 
Brāhmaṇas, kṣatriyas, vaiśyas and śūdras are distinguished by the qualities born of their own natures in accordance with the material modes, O chastiser of the enemy.