Mbh 7.136.1c

Indeed, those arrows winged with gold, piercing through the hearts of thy sons, looked beautiful, O monarch, as they passed into the sky, like birds of excellent plumage. Decked with gold and covered all over with blood, those arrows, O king, drinking the blood of thy sons passed out of their body. Pierced in their vital limbs by means of those arrows, they fell down on the earth from their cars, like tall trees growing on mountain precipices, broken by an elephant. The seven sons of thine that were thus slain were Satrunjaya, and Satrusaha, and Chitra, and Chitrayudha, and Dridha, and Chitrasena and Vikarna. Amongst all thy sons thus slain, Vrikodara, the son of Pandu, grieved bitterly from sorrow for Vikarna who was dear to him. And Bhima said, “Even thus was the vow made by me, viz., that all of you should be slain by me in battle. It is for that, O Vikarna, that thou hast been slain. My vow hath been accomplished. O hero, thou camest to battle, bearing in mind the duties of a Kshatriya. Thou wert ever engaged in our good, and especially in that of the king (our eldest brother). It is scarcely proper, therefore, for me to grieve for thy illustrious self.” Having slain those princes, O king, in the very sight of Radha’s son, the son of Pandu uttered a terrible leonine roar. That loud shout of the heroic Bhima, O Bharata, informed king Yudhishthira the Just that the victory in that battle was his. Indeed, hearing that tremendous shout of Bhima armed with the bow, king Yudhishthira felt great joy in the midst of that battle. The gladdened son of Pandu, then, O king, received that leonine shout of his brother with sounds and other musical instruments. And after Vrikodara, had sent him that message by the sign agreed upon, Yudhishthira, that foremost of persons acquainted with weapons, filled with joy, rushed against Drona in battle. On the other hand, O king, beholding one and thirty of thy sons slain, Duryodhana recollected the words of Vidura.