God had informed all His prophets of the qualities of the Final Prophet: His place of birth, His place of residence, the signs of His time of Prophethood and migration, the marks He would have on His body, the characteristics He would exhibit in His conduct, the distinctions found in His Sharia (Divine law), and so on. God had commanded the prophets to inform their communities of these attributes and to take a covenant from their people, promising that when this prophet, with these qualities and characteristics, would be sent, they would believe in him.
These details remained in the heavenly scriptures and were not altered. They were preserved in the hands of Jewish and Christian scholars. (Even today, some of these details can still be found in certain religious books). Wherever Jewish and Christian scholars were, they would explain these prophecies in full detail.
Among these, the Jewish scholars in Medina had spread the news, telling that this prophet would migrate to their city. That is why when the people of Medina encountered the Prophet in Mecca, they recognized him as the very prophet the Jews had foretold, and they believed in him.
A few years before the appearance of Islam, a man from the Jewish community of Sham (Syria), named Ibn Hayban, traveled to Medina. Those who had seen him spoke highly of his virtues, saying: “Whenever we were struck by drought and needed rain, we would cling to him and ask him to pray for the rain. He would pray, and clouds would appear in the sky, and rain would pour down on us. This happened several times. Because of this, Ibn Hayban had great respect and influence among the Jewish community of Medina.”
One day, the Jews heard that Ibn Hayban was near the end of his life. The Jews gathered around him, and he said to them: “O Jews, do you think that what has brought me from the prosperous and blessed land of Sham to this poor country?”
They all replied, “You know better.”
Ibn Hayban said: “I came from Sham to wait for the prophet whose advent is imminent. This city is the place of his migration. I hoped to find him and follow him. Unfortunately, my hope is shattered with my death. If you hear any news about him, do not allow anyone to precede you in embracing him.”
Ibn Hayban finished his final words and passed away.
The morning after the Banu Qurayza (a Jewish tribe of Medina) were defeated, three young Jews by the names of “Thalabah”, “Asid”, and “Asad”, who had not yet been deeply entrenched in customs, remembered the words of Ibn Hayban. They said to their families: “By God, this man is the very prophet Ibn Hayban described to us. Fear God and follow him.”
The Jews replied, “No, this man is not him.”
The three young men insisted again: “Yes, by God, this man is surely the one.”
They then left their fortresses and joined the army of Islam, embracing the Islamic faith.
(Taken from the book The Role of the Imams in Reviving Religion, by Allama Sayyid Murtadha Askarī, with slight modifications)