And slightly related perhaps, the Wikipedia entry for the origins of kashiwade, the "hands pressed together in prayer" done in front of Shinto Shrines.

DeepL automatic translation:

The Wei Shi-Wa-jin Den (the biography of Wei Shi-Wa-jin) describes the custom of the Japanese people in the Yamatai Kingdom and elsewhere as "見大人所敬 但搏手以當脆拝", which means that they clapped their hands instead of kneeling in worship to noble persons, indicating that they also clapped their hands to people at that time. In ancient times, clapping was performed for both gods and people, but it was no longer performed for people, leaving only for gods. It is also believed that ancient people clapped their hands when greeting people to show that they had no weapons in their hands, i.e., that they had no hostile intentions, and to express their respect for the other person [source needed].

The common theory is that the name "kashiwade" is due to misidentification or confusion of the character for "beat" with "kashiwa" [14]. Another theory is that it is related to "kashiwade," a cook at court[15], or that the shape of the hands together was made to resemble an oak leaf. In this case, the ninja hand is said to be used to avoid yomozuhegui (黄泉戸喫/黄泉竈食ひ)[16].