Garudapurana 1.196.2

1.196.2

pādayorjānunorūrvorudare hṛdyathorasi /
mukhe śirasyānupūrvamoṅkā rādīni vinyaset //

Upon the feet, knees, thighs, belly, heart, and chest, / on the mouth, and on the head, one should successively deposit the syllables beginning with Oṃ;