Reference for Bekhorot 35:42

והשני ירעה עד שיסתאב וחייב במתנות ורבי יוסי פוטר:

For R'Jose exempts only where the priest has [a beast] in its stead, in which case [the Sages] put one who has not taken possession, in the position of one who had taken possession.

Jastrow

Jastrow

Jastrow