Cleansing of the Nadis and Chakras for retention of Prana
Suddhameti yada sarvam nadichakram malakulam /
Tadaiva jayate yogi pranasamghrahane kshamah//(Chapter -2, Verse 5).
When all the nadis and chakras which are full of impurities are cleansed, then the hatha yogi is able to retain prana. (Chapter -2, Verse 5).