Charak Samhita
विधिरेषोऽवपीडस्य कार्यः प्रध्मापनस्य तु। तत् षडङ्गुलया नाड्या धमेच्चूर्णं मुखेन तु॥१०७॥
As regards pradhmapana (powder inhalation), the medicinal powder should be blown by mouth through a 6 Angula long tube.
english translation
vidhireSo'vapIDasya kAryaH pradhmApanasya tu। tat SaDaGgulayA nADyA dhameccUrNaM mukhena tu॥107॥
hk transliteration by Sanscript