Numbers 23:30

And Balak did as Balaam had said, and offered a bullock and a ram on every altar.

Cross-reference

Numbers 23:2 describes the same ritual at an earlier location — Balak builds seven altars and offers a bull and ram on each.

Numbers 22:17 shows Balak promising to do whatever Balaam says — here he fulfills that promise by offering sacrifices.

Numbers 22:40 records Balak's earlier sacrifice of oxen and sheep — here he again sacrifices, now on seven altars.