Rashi on Numbers 28:19/רש"י על במדבר כ״ח:י״ט

1פרים BULLOCKS — in allusion to Abraham, as it is said, (Genesis 18:7) “And unto the herd (the bullock) Abraham ran”,

2אילים RAMS — in allusion to the ram of Isaac (Genesis 22:13).

3כבשים LAMBS — in allusion to Jacob, as it is said, (Genesis 30:40) “And the lambs did Jacob set aside”. I saw this in the work of R. Moses the Preacher (see Rashi on Numbers 7:21).