Can anyone help me find this story about Ananda?

I read an account that Ananda went from the Deer Park to teach people, and taught a blacksmith to focus on the impurity of the body, and a washerwoman to count breaths, and they both became 'icchantikas'. Buddha told him to swap the teachings, and they both became arhats. I read it in passing, I think wjile researching the icchantika concept and I've been unable to relocate it. But I often think of the story, as illustrating the need for the right teaching for the specific person, and I'd love to be able to properly reference it.. Maybe I should search for keywords in an online Tipitaka..?