Charak Samhita
श्रेयो मृद्वसकृत्पीतमल्पबाधं निरत्ययम्। न चातितीक्ष्णं यत् क्षिप्रं जनयेत्प्राणसंशयम्॥६८॥
It is always best & safe to use the mridu shodhana dravyas (mild purification) repeatedly as they are less harmful rather than using the tikshana shodhana dravyas (strong purification), which may cause sudden threat to life.
english translation
zreyo mRdvasakRtpItamalpabAdhaM niratyayam। na cAtitIkSNaM yat kSipraM janayetprANasaMzayam॥68॥
hk transliteration by Sanscript