Internal austerities- The Tapa (austerity) which, influences the Karma-śarīra (subtle most body formed by Karma-pudgalas (material clusters qua Karma)) and which, because of comprising mainly of the inhibition of the Citta (psychic causes of bondage of Karma), becomes intrinsically effective in annihilation of Karma.
ābhyantaraṃ- cittanirodhaprādhānyena karmakṣapaṇahetutvāt.
(Sama 6.4 Vṛ Pa 12)