The great sage Viśvāmitra saw that Mahārāja Hariścandra, along with his wife, was truthful, forbearing and concerned with the essence. Thus he gave them imperishable knowledge for fulfillment of the human mission.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
शुनःशेफस्य माहात्म्यमुपरिष्टात्प्रचक्ष्यते । सत्यसारां धृतिं दृष्ट्वा सभार्यस्य च भूपतेः
śunaḥśephasya māhātmyamupariṣṭātpracakṣyate | satyasārāṃ dhṛtiṃ dṛṣṭvā sabhāryasya ca bhūpateḥ
SB 9.7.24