Which institution do I contact for this?

I have a transfer of money occurring monthly from a checking account at one institution to a savings account at another. I vaguely recall that I set it up online, but I don’t remember whether I did it through the bank that’s sending or receiving the money, and I can’t find anything on either website to stop it. Any idea how I can figure out which of them I should call to get it stopped? The less time I can spend on the phone with customer services, the happier I am.