Garudapurana 1.11.21

1.11.21

hṛdayādīni pūrvādicaturdigdalayogataḥ /
madhye netraṃ tu koṇeṣu astramantraṃ nyasettataḥ //

the heart and other [limbs] by connection with the petals of the four directions beginning with the east; / then one should place the eye in the middle, and the weapon-mantra in the corners;