“Doubt burns up everything, including the doubter.
To banish it bow down to the Lord.”
– T Krishnamacharya’s commentary to Yoga Sūtra Chapter One verse 5

“Saṃśaya (Doubt) is the Fire that consumes Wisdom.”
– T Krishnamacharya commentary on Bhagavad Gītā Chapter Four verse 40

“Jñāna is like a sword to cut away Saṃśaya.”
– T Krishnamacharya commentary on Bhagavad Gītā Chapter Four verse 41

“What good is the sword of wisdom (Jñāna Asinā),
to cut away the chains of doubt (Saṃśaya),
if the holder is too weak to bear it.”
– T Krishnamacharya commentary on the Bhagavad Gītā Chapter Four verse 42

“Doubts always arise.
There is no doubt about that!”
– TKV Desikachar ‘Antarāyāḥ, Obstacles to progress, Techniques to Overcome them’
Religiousness in Yoga Chapter Fourteen Page 208