Reference for Ketubot 202:19

ה"ד אי דאמר להו אתם עדיי מ"ט דר"ל דקפטר אי דלא אמר להו אתם עדיי מ"ט דרבי יוחנן דקמחייב

What is the case? If [it refers to a case] where the man said to them, “You are my witnesses,” what is the reason of Resh Lakish who holds him to be exempt? If [it is a case] where he did not say to them, “You are my witnesses,” what is the reason of R. Yohanan who holds him liable?

Jastrow