2 Samuel 4:4 (BSB)

And Jonathan son of Saul had a son who was lame in his feet. He was five years old when the report about Saul and Jonathan came from Jezreel. His nurse picked him up and fled, but as she was hurrying to escape, he fell and became lame. His name was Mephibosheth.

From 2 Samuel 4. Also in the ESV.

Commentary on 2 Samuel 4:4

• Matthew Henry (Presbyterian), Matthew Henry's Complete Commentary on 2 Samuel 4:1-8: Here is, I. The weakness of Saul's house. Still it grew weaker and weaker. 1. As for Ishbosheth, who was in possession of the throne, his hands were feeble, Sa2 4:1. All the strength they ever had was from Abner's support, and now that he was dead he had no spirit left in him.
• John Gill (Reformed Baptist), Exposition of the Old and New Testaments on 2 Samuel 4:4: And the sons of Rimmon the Beerothite, Rechab and Baanah, went,.... From Gittaim, where they were sojourners, Sa2 4:3; or from the army, where they had commissions, wherever it was: and came, about the heat of the day; the middle of the day, at noon, as follows: to the house of Ishbosheth; which was at Mahanaim: who lay on a bed at noon; as was...
• Adam Clarke (Methodist), Clarke's Commentary on the Bible on 2 Samuel 4:4: He fell, and became lame - Dislocated his ankle, knee, or thigh; which was never after reduced; and thus he became lame. Lovely Jonathan! unfortunate in thy life, and in thy progeny.
• Keil & Delitzsch (Lutheran), Biblical Commentary on the Old Testament on 2 Samuel 4:4: 2Sa 4:4 Before the historian proceeds to describe what the two Beerothites did, he inserts a remark concerning Saul’s family, to show at the outset, that with the death of Ishbosheth the government of this family necessarily became extinct, as the only remaining descendant was a perfectly helpless cripple. He was a son of Jonathan, smitten (i.e., lamed) in his feet.