This is one of the Targum's most humane glosses, tucked into a genealogy verse no one usually stops for. Targum Pseudo-Jonathan on Genesis 25:19 says: "These are the generations of Isaac bar Abraham. And because the appearance of Isaac resembled the appearance of Abraham, the sons of men said, In truth Abraham begat Isaac."
Stop and imagine the scene. Sarah had been barren for decades. Abraham was a hundred years old when Isaac was born. The gossip in the villages around Hebron was predictable and mean. Isaac, the whisperers said, must really be the son of Abimelech or someone else — some hidden father, some secret arrangement.
So God, in the Targum's reading, did a small miracle in the boy's face. Isaac grew up looking exactly like his father. Same eyes, same brow, same bearing. When people saw the two of them walking together, the rumor died in their mouths. "In truth Abraham begat Isaac" — the resemblance was proof.
The tradition from Bava Metzia 87a makes this explicit. Before Isaac, children did not always look strikingly like their fathers. When Isaac was born, God stamped him with Abraham's likeness specifically to silence the slanderers.
The Maggid's lesson is quiet and kind. God cares about the reputation of the righteous. Not vainly — truly. Abraham and Sarah had endured twenty-five years of shame as they waited for the promised child. When the child finally came, God made sure no one could rob the victory with a sneer.
Sometimes the miracle is a healing. Sometimes the miracle is a family resemblance that ends a rumor. Both count.