kāyendriyasiddhir aśuddhikṣayāt tapasaḥ [YS 2.43]

nirvartyamānam eva tapo hinasty aśuddhyāvaraṇamalaṃ tadāvaraṇamalāpagamāt kāyasiddhir aṇimādyā. tathendriyasiddhir dūrāc chravaṇadarśanādyeti.