A tengu teaches correct Buddhist magical signs (inkei)
"A Buddhist priest on his way to Mutsu province stopped in a mountain village for a night's lodging, but could find no place available to stay. 'There's an old, small, abandoned Buddhist temple on the side of this mountain where you might stop, but it is believed that tengu live there,' warned the villagers.
Not feeling afraid at all of stories of tengu, the priest climbed the side of the mountain to the little abandoned temple where he seated himself on the platform behind the statue of the Buddha.
That night a crowd of people came down from the top of the mountain to the little abandoned temple. The frightened priest performed the Marishitenhõbyõ-in (mudrā of invisibility) and watched quietly from behind the statue.
He saw a fat priest with an unusually glowing, white appearance pull up in a palanquin and enter the temple with twenty or thirty attendants. He sent the attendants out to amuse themselves in front of the temple and then turned and called out to the priest hiding behind the statue of Buddha:
'Your inkei is all wrong. Come here and I will teach you.' So the glowing priest instructed him, warning him that he must not ever reveal the magical sign to any who were not worthy of it's power. The priest again sat behind the Buddha statue and formed the inkei.
'Good, good! Now you are invisible.' said the glowing white priest. Afterward he called his companions back to the temple, where they entertained themselves with dance and then returned to the mountain top."
It was later revealed that the glowing white priest and his attendants were tengu. Having been Buddhist priests in a previous life, tengu are more knowledgable than priests with less experience.
From the Tengu Zõshi (1296)