2 Samuel 19:2 (BSB)

And that day’s victory was turned into mourning for all the people, because on that day they were told, “The king is grieving over his son.”

From 2 Samuel 19. Also in the ESV.

Commentary on 2 Samuel 19:2

• Matthew Henry (Presbyterian), Matthew Henry's Complete Commentary on 2 Samuel 19:1-8: Soon after the messengers had brought the news of the defeat and death of Absalom to the court of Mahanaim, Joab and his victorious army followed, to grace the king's triumphs and receive his further orders. Now here we are told, I.
• John Gill (Reformed Baptist), Exposition of the Old and New Testaments on 2 Samuel 19:2: And the victory that day was turned into mourning unto all the people,.... They also mourned too, instead of expressing joy upon the occasion: for the people heard say that day how the king was grieved for his son; this report was spread among them, which damped their joy, and hindered them from giving any tokens of it, as were usual at such times.
• Geneva Bible Notes (Reformed), Geneva Bible Study Notes on 2 Samuel 19:1-3: And the king was much moved, and went up to the chamber over the gate, and wept: and as he went, thus he said, O my son Absalom, my son, my son Absalom! would God I had died for thee, O Absalom, my son, my son! (l) Because he considers both the judgment of God against his sin, and could not otherwise hide his fatherly affection for his son.
• Adam Clarke (Methodist), Clarke's Commentary on the Bible on 2 Samuel 19:2: The victory - was turned into mourning - Instead of rejoicing that a most unnatural and ruinous rebellion had been quashed, the people mourned over their own success, because they saw their king so immoderately afflicted for the loss of his worthless son.