drstva mahadbhutam raja
raja pandu-sutah kratau
muninam srnvatam idam
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
O King, at the Rajasuya sacrifice, Maharaja Yudhisthira, the son of Maharaja Pandu, personally saw Sisupala merge into the body of the Supreme Lord, Krsna. Therefore, struck with wonder, he inquired about the reason for this from the great sage Narada, who was seated there. While he inquired, all the sages present also heard him ask his question.