In Rig Veda Mandala 10 Sukta 112, sloka 9 it says:
नि षु सीद गणपते गणेषु तवामाहुर्विप्रतमंकवीनाम |
न रते तवत करियते किं चनारे महामर्कंमघवञ्चित्रमर्च ||
Lord of the hosts, sit down among us, they call thee the greatest sage among sages; without thee nothing is done in the distance; great, wondrous, Maghavan, is the hymn I sing thee.
He is again praised as the sage among sages in mandala 6, Sukta 32, sloka 3:
स वह्निभिर्र्क्वभिर्गोषु शश्वन मितज्ञुभिः पुरुक्र्त्वा जिगाय |
पुरः पुरोहा सखिभिः सखीयन दर्ळ्हा रुरोज कविभिः कविः सन ||
Achiever of great deeds, with priests who kneel and laud him, he hath conquered in the frays for cattle,
And broken down the forts, the Fort-destroyer, a Friend with friends, a Sage among the sages.
In Mandala 6, Sukta 30, sloka 1, Sage Bharadvaja says:
Indra increased in might in display of valour; He the lord of all, the imperishable, bestows felicity to his worshipers. Indra surpasses both the worlds, a mere portion of him is equal to both heaven and earth.
In Mandala 7, Sukta 20, sloka 6, Sage Vasishta says:
He who devotes himself to the mighty Indra never falls to ruin, nor will he perish!;
The protector of sacred rites, the progeny of sacrifice, bestows prosperity on him who offers to Indra praises and prayers with sacrifice.
In Mandala 8 , Sukta 1, sloka 6, Sage Kanva says:
You are more precious Indra, than my own father, or than my unaffectionate brother; you oh giver of dwellings are equal to my mother, for you both bless me with prosperity.
In Satapatha Brahmana Kanda 6, Adhyaya 1, Brahmana 1 , it is written:
Verily, in the beginning there was here the non-existent . As to this they say, 'What was that non-existent?' The Rishis, assuredly,it is they that were the non-existent . As to this they say, 'Who were those Rishis?' The Rishis, doubtless, were the vital airs: inasmuch as before (the existence of) this universe, they, desiring it, wore themselves out (rish) with toil and austerity, therefore (they are called) Rishis.
This same vital air in the midst doubtless is Indra. He, by his power (indriya), kindled those vital airs from the midst; and inasmuch as he kindled (indh), he is the kindler (indha): the kindler indeed, him they call 'Indra' mystically , for the gods love the mystic. They (the vital airs), being kindled, created seven separate persons (purusha).