Mahabharata Udyoga Parva Chapter 10:2

Mahabharata Udyoga Parva Chapter 10:2 And the mighty Vritra having heard the words of the saints, bowed his head unto them. And the Asura (thus) spoke, "What you, O highly-gifted beings, and also all these Gandharvas are saying, I have heard. Ye stainless beings, hear also what I have got to say. How can there be peace between us two, Indra and myself? How can there be friendship, ye gods, between two hostile powers?" The Rishis said, "Friendship among righteous persons happens at a single meeting. It is a desirable object. Thereafter will happen what is fated to be. The opportunity of forming friendship with a righteous person should not be sacrificed. Therefore, the friendship of the righteous should be sought. The friendship of the righteous is (like) excellent wealth, for he that is wise would give advice when it is needed. The friendship of a good person is of great use; therefore, a wise person should not desire to kill a righteous one. Indra is honoured by the righteous, and is the refuge of magnanimous persons, being veracious and unblamable, and knows what virtue is, and is possessed of a refined judgment. Let there be eternal friendship between thee and Indra, as described above. In this way, have faith (in him); let not thy heart be differently inclined. Salya said, 'Hearing these words of the great Rishis, the illustrious Asura spoke to them, "No doubt, the Rishis, endued with supernatural powers, are to be respected by me. Let what I am going to say, ye gods, be performed in its entirety; then I shall do everything that (these) best of Brahmanas have said to me. Ye lords of the Brahmana race, ordain so that Indra himself or the gods do not kill me by what is dry, or wet; by stone, or by wood; by a weapon fit for close fight, or by a missile; in the day time, or at night. On those terms eternal peace with Indra would be acceptable to me,"—Very good! was what the Rishis told him, O best of Bharata race. Thus peace having been concluded, Vritra was very much pleased. And Indra also became pleased though constantly occupied with the thought of killing Vritra. And the chief of the deities passed his time in search of a loophole, uneasy (in mind). And on a certain day when it was evening and the hour awful, Indra caught sight of the mighty Asura on the coast of the sea. And he bethought himself of the boon that was granted to the illustrious Asura, saying, "This is the awful evening time; it is neither day, nor night; and this Vritra, my enemy, who hath stripped me of my all, must undoubtedly be killed by me. If I do not kill Vritra, this great and mighty Asura of gigantic frame, even by deceit, it will not go well with me.