Bhagavad Gita 17.14

देवद्विज्गुरुप्रज्ञपूजनं शौचमार्जवम् |
ब्रह्मचर्यमहिंसा च शरीरं तप उच्यते

Translation

When worship of the Supreme Lord, the Brahmins, the spiritual master, the wise, and the elders is done with the observance of cleanliness, simplicity, celibacy, and non-violence then this worship is declared as the austerity of the body.