The first of the companions of the Prophet who came to us (in Medina), were Mus'ab bin 'Umar and Ibn Um Maktum, and they started teaching us the Qur'an. Then came 'Ammar, Bilal and Sad. Afterwards 'Umar bin Al-Kkattab came along with a batch of twenty (men): and after that the Prophet came. I never saw the people of Medina so pleased with anything as they were with his arrival, so that even the little boys and girls were saying, "This is Allah's Apostle who has come." He (the Prophet ) did not come (to Medina) till I had learnt Surat Al-Ala and also other similar Suras.
Sahih al-Bukhari, Vol. 6, Book of Prophetic Commentary on the Qur'an, Hadith 465
Sahih al-Bukhari, Book of Prophetic Commentary on the Qur'an, Hadith 465