攝大毘盧遮那成佛神變加持經入蓮華胎藏海會悲生曼荼攞廣大念誦儀軌供養方便會 2.46

2.46

前印申火屈，火風並如鉤，
是名如來心。

From the previous mudrā, extend the fire [finger] and bend it, so that fire and wind are both like hooks;
this is called the Tathāgata-Heart.