Parashas Naso · Passuk 7:15
one bull of the herd, one ram, and one lamb in its first year, for a burnt offering;
Chabad.org — English translation + Rashi
Source: Menachos 61b.
English: “One young bull\ldots” — what does “one bull and one ram” teach? One bull — that there was none like it in his herd.
In context: Each animal was choice, without peer in the prince’s flock; the midrash reads the singularity as excellence.
Custom
Chazal interpret the repeated “one” as indicating that each animal was the finest of its kind.