Bhagavad Gītā Chapter Six verse 46

tapasvibhyo ’dhiko yogī jñānibhyo ’pi mato ’dhikaḥ |
karmibhyaś cādhiko yogī tasmād yogī bhavārjuna ||

tapas - self-discipline

Commentaries and Reflections

T Krishnamacharya:

Tapas is Proper Diet, Mantra Chanting and Self-Inquiry.