Skandapurana 16.107.31

16.107.31

vakāraṃ hṛdi madhye tu rekāraṃ pārśvayordvayoḥ ..
ṇikāraṃ dakṣiṇe kukṣau yakāraṃ vāmasaṃjñite .. 31 ..

the syllable 'va' in the middle of the heart, the syllable 're' on the two sides, / the syllable 'ṇi' in the right flank, and the syllable 'ya' in that known as the left;