Reference for Ketubot 222:20

רב חייא בר אדא מקרי דרדקי דר"ל הוה איפגר תלתא יומי ולא אתא כי אתא א"ל אמאי איפגרת

Hiyya b. Adda was a teacher of Scripture for the children of Resh Lakish. [On one occasion] he was delayed for three days and he did not come [to teach the children].

Jastrow