Al-Matalib al-'Aliyah 3855 — The People of the Book bearing witness

It is narrated from Sayyiduna al-Faltan bin Asim al-Jarmi (may Allah be pleased with him) that he said: We were sitting with the Prophet (peace and blessings be upon him) in the mosque when suddenly his (peace and blessings be upon him) blessed gaze became fixed on a man walking in the mosque. That man called out: "Here I am, O Messenger of Allah!" and whenever he spoke to him (peace and blessings be upon him), he would only say: "O Messenger of Allah!" The narrator said: The Messenger of Allah (peace and blessings be upon him) asked him: "Do you bear witness that I am the Messenger of Allah?" He replied: "No." He (peace and blessings be upon him) asked: "Do you read the Torah?" He said: "Yes." He (peace and blessings be upon him) asked again: "And the Injil (Gospel) too?" He replied: "Yes, and the Qur'an too; by the One in whose hand is my soul, if I wished, I could recite it as well." The narrator said: Then he (peace and blessings be upon him) adjured him (by the truth) and asked: "Do you find me written as a prophet in the Torah and the Injil?" He said: "I will tell you how the matter stands: we find (in our books) attributes like yours, a bearing like yours and the signs of the place of your emergence. We had hoped that this prophet would be from among us, but when you emerged we feared that you might be that prophet; then, when we looked, (in our view) you were not he." Then the Messenger of Allah (peace and blessings be upon him) said: "By the One in whose hand is the soul of Muhammad (peace and blessings be upon him), I am indeed he (the promised Prophet), and they (who are mentioned in the books) are my Ummah, and their number will exceed seventy thousand and seventy thousand (that is, they will be countless)."
The chain of this hadith is hasan (good); Imam Ahmad narrated it in his Musnad (16162) and Imam al-Tabarani in al-Mu'jam al-Kabir (825).