From this videoconference talk from 21 June 2019, Ajahn Anan discusses the history of "Sadhu".

An excerpt: "The monks anumodana with the lay people, the lay people anumodana with the monks. Each person gives their anumodana and is joyous at the goodness that all of us have done. And this sadhu has a history behind it."

Note: One can read Dhamma talk transcripts at the Wat Marp Jan 'Reflections' page, which also includes questions and answers with Ajahn Anan, which are not in the audio files. See: https://watmarpjan.org/en/dhamma-reflections/reflections-archive/