Midrash for Chullin 159:10

נהי נמי דחוששין לזרע האב שה ואפילו מקצת שה לא אמרינן

In the case where a hart covered a she-goat the dispute is as to [whether] stripes [are inflicted or not]; the Rabbis holding that even though we take into consideration the seed of the male parent, since we say that the term 'sheep' includes even that which is a sheep in part only, we therefore inflict stripes upon him; whilst R'Eliezer maintains: There is only a prohibition but stripes cannot be inflicted.'

Sifrei Devarim