Yosef Karo

“ There are places that do say many slichot and everything should follow the custom. Regarding saying Avinu Malkenu on Erev Yom Kippur, there is a debate among later halakhic authorities, and my city's custom is not to say it unless Yom Kippur falls on Shabbat. Then, because we do not say Avinu Malkenu on Yom Kippur, we say it on Erev Yom Kippur in the morning. ”