2 Samuel 6:7 (BSB)

And the anger of the LORD burned against Uzzah, and God struck him down on the spot for his irreverence, and he died there beside the ark of God.

From 2 Samuel 6. Also in the ESV.

Commentary on 2 Samuel 6:7

• Matthew Henry (Presbyterian), Matthew Henry's Complete Commentary on 2 Samuel 6:6-11: We have here Uzzah struck dead for touching the ark, when it was upon its journey towards the city of David, a sad providence, which damped their mirth, stopped the progress of the ark, and for the present, dispersed this great assembly, which had come together to attend it, and sent them home in a fright. I. Uzzah's offence seems very small.
• John Gill (Reformed Baptist), Exposition of the Old and New Testaments on 2 Samuel 6:7: And David was displeased, because the Lord had made a breach upon Uzzah,.... He could not easily submit, and be reconciled to the providence; his heart was ready to rise up against God, and murmur at him for striking him dead in such an awful manner, for so small a matter as this might seem to be; and the rather, as this put a stop...
• Geneva Bible Notes (Reformed), Geneva Bible Study Notes on 2 Samuel 6:7: And the anger of the LORD was kindled against Uzzah; and God smote him there for [his] error; and there he died by the ark of God. (d) Here we see the danger it is to follow good intentions, or to do anything in God's service without his express word.
• Adam Clarke (Methodist), Clarke's Commentary on the Bible on 2 Samuel 6:7: Smote him there for his error - Uzzah sinned through ignorance and precipitancy; he had not time to reflect, the oxen suddenly stumbled; and, fearing lest the ark should fall, he suddenly stretched out his hand to prevent it. Had he touched the ark with impunity, the populace might have lost their respect for it and its sacred service, the example of Uzzah must have...