Shatapatha Brahmana 8.5.4.3

8.5.4.3

yadvevāṣāḍhāyai | iyaṃ vā aṣāḍhā hṛdayaṃ stomabhāgā asyāṃ taddhṛdayam mano dadhāti tasmādasyāṃ hṛdayena manasā cetayate sarvata upadadhāti sarvatastaddhṛdayam mano dadhāti tasmādasyāṃ sarvato hṛdayena manasā cetayate 'tho puṇyā haitā lakṣmyastā etatsarvato dhatte tasmādyasya sarvato lakṣma bhavati tam puṇyalakṣmīka ityācakṣate

And, again, why (on that) of the Ashâdhâ;--the Ashâdhâ, doubtless, is this (earth), and the Stomabhâgâs are the heart: he thus lays into this (earth) the heart, the mind: whence on this (earth) one thinks with the heart, with the mind. He lays them down on every side: he thus places the heart, the mind everywhere; whence everywhere on this (earth) one thinks with the heart, with the mind. And, moreover, these (bricks) are lucky signs: he places them on all sides; whence they say of him who has a (lucky) sign (lakshman) on every (or any) side that he has good luck (punyalakshmîka).