The first existing document about his Nyujo was "Kongobuji Konryu Shugyo Engi" written by Ningai in 968, in more than 100 years after his death, in which he described that, even 49 days after his Nyujo, his body color remained unchanged and his hair and beard continued growing.
現存する資料で空海の入定に関する初出のものは、入寂後100年以上を経た康保5年（968年）に仁海が著した『金剛峰寺建立修行縁起』で、入定した空海は四十九日を過ぎても容色に変化がなく髪や髭が伸び続けていたとされる。