The Prophet of Allah, sallallaahu ‘alayhi wa sallam, sent Mus`ab ibn `Umayr to Madinah to call people to Allah
He, sallallaahu ‘alayhi wa sallam, chose Mus`ab ibn `Umayr and sent him to be a teacher in Madinah, and to be his first ambassador. He was to teach the Muslims the basics of the religion, as well as the tenets of Islam, teach the Quran to them, and call to the path of Allah The Glorious, The Praiseworthy. That is why he was nicknamed, Al-Muqri’ (the one who teaches Quran).
Thus, we know through this that Madinah was conquered with the Quran rather than the sword.
Al-Baraa’ ibn `Aazib said
“The first to come to us was Mus`ab ibn `Umayr, and Ibn Umm Maktoom, and they both used to teach the people the Quran.”