In the Shalya Parva of the Mahabharata, before Bhima faces Duryodhana in the mace battle, Vishnu's incarnation Krishna warns Arjuna about how formidable Duryodhana will be, since Duryodhana has just been defeated in the war:
This old verse uttered by Usanas hath been heard by us. Listen to me as I recite it to thee with its true sense and meaning! "Those amongst the remnant of a hostile force broken flying away for life, that rally and come back to the fight, should always be feared, for they are firmly resolved and have but one purpose!" Shakra [Indra] himself, O Dhananjaya, cannot stand before them that rush in fury, having abandoned all hope of life.
For those who don't know, Ushanas is another name of Sukracharya, guru of the Asuras, because his mother was Bhrigu's wife Ushana AKA Kavyamata, whom I discuss here.
So my question is, where is this verse of Sukracharya quoted by Krishna from? Is it from the Vedas? The Rig Veda Anukramani provided in my answer here mentions a few hymns which were heard from the gods by Sukracharya, but at first glance I couldn't find this verse there. Is it from something other than the Vedas?