首楞嚴義疏注經 1.515

1.515

摩頂，安慰也。阿難疑問，將謂無心。今若開示，必知體遍。冥合此理，了法無生，印可決定，名無生忍。得此忍時，通達一切法門，成就一切佛法。此非小緣，故佛安慰，警動其意，是故摩頂也。

Rubbing the crown is consoling him. Ānanda raised doubts, thinking there was no mind. Now if [the Buddha] instructs him, he will certainly know that its substance is pervasive. When in tacit accord with this principle, realizing that dharmas are non-arisen, and definitively confirming it, this is called the forbearance of non-arising. When attaining this forbearance, one thoroughly penetrates all dharma-gates and accomplishes all buddha-dharmas. This is no small condition; therefore the Buddha consoles him and stimulates his mind, and so rubs his crown.