Reference for Ketubot 107:17

רב כהנא מתני וכן בלקיט ומנח בה סימנא יתמא וארמלתא שלח ופוק

Kahana taught: And so [are their opinions] in the case of a hired worker; and he made this mnemonic: A widow and an orphan—strip them and go out.

Jastrow