Not only it was recorded in Chinese history books such as "Gishiwajinden" (literally, an 'Account of the Wa' in "The History of the Wei Dynasty") and "Zuisho; Suishu" (the Book of the Sui Dynasty), it was already established as a common law as it was referred to in Shasho (decree of amnesty) which was used during the time of the Emperor Temmu ("Nihonshoki" (Chronicles of Japan), the Article of Mizuno-e, the eighth month of the fifth year of the Emperor Temmu).
『魏志倭人伝』や『隋書』などの中国の歴史書に書かれているだけではなく、天武天皇期に用いられた「赦書」にも登場する（『日本書紀』天武天皇5年8月壬子条）など、慣習法として確立していた。