The works of Ādi Śaṅkarācārya

Praśnottararatnamālikā

Verse 44

कस्मात् सिद्धिः तपसः बुद्धिः क्व नु भूसुरे कुतो बुद्धिः ।वृद्धोपसेवया के वृद्धा ये धर्मतत्त्वज्ञाः ॥ ४३ ॥

In plain words

What brings austerity to its fulfillment? Wisdom. Where is that wisdom found in a seeker? And from where does such wisdom come? From serving the wise elders. And who are the true elders? Those who have realized the essential truth of Dharma.

Close to the Sanskrit

From what is the accomplishment of austerity? [From] intellect. Where indeed is [this] intellect in a brahmin? From where is [this] intellect? From the service of elders. Who are the elders? Those who are the knowers of the essence of Dharma.