Parashas Metzora · Passuk 15:15
Chabad.org — English translation + Rashi
Torah Temima points to Yoma 41a.
English: “And the kohen shall make them” — Rav Chisda said: Nest-pairs are designated only either at the owners’ taking or at the kohen’s performance.
Designation of bird-pair roles
Chazal allow the chatas/olah assignment of the two birds to be fixed either when the owner takes them or when the kohen offers them.