俱舍論記 8.164

8.164

「若此契經至固唯中有」者，第三掌馬族經。父祖皆執掌馬，故名掌馬族。此人彼族中生，故以為名。佛為掌馬族人說此經。經言中有正現前者，四姓之中為是何姓？於四方面為何方來？前蘊已壞不可言來，此所言來定唯中有。婆羅門，此云靜志。剎帝利，此云守田種。吠舍，此是興事種。戍達羅，是營田種。

Regarding "If this discourse [...] it is definitely only the intermediate existence": this is the third, the Aśvalāyana-sūtra. His father and grandfather both had charge of horses; hence the clan is called the Aśvalāyana ("Horse-controller clan"). This person was born in that clan, so he was named after it. The Buddha spoke this discourse for the person of the Aśvalāyana clan. The discourse asks: of the four castes, to which caste does the intermediate existence right now present before you belong? From which of the four directions has it come? The prior aggregates having already perished, they cannot be said to come; that which is said to come here is definitely only the intermediate existence. "Brāhmaṇa" is translated here as "one of quiet resolve." "Kṣatriya" is translated here as "the caste that protects the fields." "Vaiśya" is the caste of commercial affairs. "Śūdra" is the caste of field labor.