The secret only two men knew

Umayr ibn Wahb walked into Madinah carrying his sword and telling anyone who asked that he had come to ransom his son and to see how the captives were being treated.

Umar ibn al-Khattab did not believe him. He had known Umayr in Makkah as one of those most set against the Muslims, and told the Prophet ﷺ so, urging that he be watched closely and disarmed.

The Prophet ﷺ had Umayr brought in and asked him plainly what had brought him. Umayr repeated the story about his son.

The Prophet ﷺ then told him, in substance, what he and Safwan ibn Umayyah had agreed between themselves in Makkah — the killing, the arrangement over his debts and his family — a conversation the two of them believed no one else had heard.

Umayr had no answer for that except to accept it as true, and he accepted Islam there.

He asked to be taught the basics of the religion and then went back to Makkah, not to hide what had happened to him but to call the people there to Islam himself.