Mbh 8.71.1

"Sanjaya said, 'Having heard these joyful words of king Yudhishthira, Govinda of virtuous soul, that delighter of the Yadus, then addressed Partha. The latter, however, having at the instance of Krishna addressed those words unto Yudhishthira, became exceedingly cheerless for having committed a trivial sin. Then Vasudeva, smiling, said unto the son of Pandu, "What would have been thy condition, O Partha, if, observant of virtue thou hadst slain the son of Dharma with thy sharp sword? Having only addressed the king as thou, such cheerlessness hath possessed thy heart. If thou hadst slain the king, O Partha, what wouldst thou have done after that? Morality is so inscrutable, especially by persons of foolish understanding. Without doubt great grief would have been thine in consequence of thy fear of sin. Thou wouldst have sunk also in terrible hell in consequence of the slaughter of thy brother. Gratify now this king of virtuous behaviour, this foremost of all practisers of virtue, this chief of Kuru's race. Even this is my wish. Gratifying the king with devotion, and after Yudhishthira will have been made happy, we two will proceed against the car of the Suta's son for fighting him. Slaying Karna today with thy keen shafts in battle, do thou, O giver of honours, give great happiness to Dharma's son. Even this, O mighty-armed one, is what I think to be suitable to this hour. Having done this, thy purpose will be achieved." Then Arjuna, O monarch, in shame, touched king Yudhishthira's feet with his head. And he repeatedly said unto that chief of the Bharatas, "Be pleased with me, Forgive, O king, all that I have said from desire of observing virtue and from fear of sins."'"