Manusmriti

siva.sh/manusmriti/6/70

प्राणायामा ब्राह्मणस्य त्रयोऽपि विधिवत् कृताः । व्याहृतिप्रणवैर्युक्ता विज्ञेयं परमं तपः ॥ ७० ॥

sanskrit

Three suppressions of the breath even, performed according to the rule, and accompanied with the (recitation of the) Vyahritis and of the syllable Om, one must know to be the highest (form of) austerity for every Brahmana.

english translation

prANAyAmA brAhmaNasya trayo'pi vidhivat kRtAH | vyAhRtipraNavairyuktA vijJeyaM paramaM tapaH || 70 ||

hk transliteration by Sanscript