佛說觀佛三昧海經 1.49

1.49

「若有比丘及比丘尼、諸優婆塞、優婆夷等，欲觀佛髮當作是觀，不得他觀。若他觀者名為邪觀、名為狂亂、名為失心、名為邪見、名顛倒心，設得定者無有是處。如是父王，佛真髮相事實如此。

"If there are monks, nuns, upāsakas, and upāsikās who wish to contemplate the Buddha's hair, they must practice this contemplation; they must not contemplate otherwise. If they contemplate otherwise, it is called erroneous contemplation, it is called madness and confusion, it is called loss of mind, it is called wrong view, it is called an inverted mind; even if they were to attain absorption, it would be impossible. Thus, father the king, such is the factual reality of the Buddha's true mark of the hair.