Shiva Purana
यकरादिसकारांतान्न्यसेत्सप्तसु धातुषु ॥ हंकारं हृदयस्यांतः क्षकारं भ्रूयुगांतरे ॥ २९ ॥
The syllables ending in yakara and s should be placed in the seven elements. The syllable ham is situated within the heart, and the syllable k is situated between the eyebrows.
english translation
yakarAdisakArAMtAnnyasetsaptasu dhAtuSu ॥ haMkAraM hRdayasyAMtaH kSakAraM bhrUyugAMtare ॥ 29 ॥
hk transliteration by Sanscript