This episode about the vengeful ghost of Sutoku-in often appears in "Heike Monogatari," "Taiheiki (the chronicle describing the civil war between the Northern and Southern Dynasties in the late fourteen century)," and even in history books like "Hyakurensho," so there is no doubt that it was in fact believed at that time.
この崇徳院の怨霊にまつわる話は『平家物語』『太平記』にもたびたび引き合いに出され、『百錬抄』など、史書にも見えているため、当時実際に信じられていたことについては疑いはない。