Al-Hafizh Ibn Katheer in his book Al-Bidayah Wan-Nihayah summarized Ahmad Al Khani tells the beginning of the Ansar converted to Islam.
When Allah wanted the emergence of His chosen religion and strengthened His Prophet, The Prophet Muhammad (pbuh) set out to meet many people from among The Ansar during the Hajj season.
The Prophet (ï·º) said to them, “Who are you all?’ They said, “We are khazraj people.”
The Prophet (ï·º) asked, “What is it from the Jewish government?” They said, “Yes.”
The Prophet (ï·º) said, “What if you sit down for a while so that I can talk to you?” They said, “All right.”
Then they sat down with the Prophet (ï·º) to call them to worship Allah SWT, show islam to them, and recite the Qur’an to them.
Then they said to one another, “O people, by Allah, you know he is the Prophet, as the Jews promised you, and they did not precede you from meeting him.”
They say, “A Prophet has been sent now. It has overshadowed his time and we follow it. We fought with him as we attacked the Aad and Iram.”
The People of Anshar fulfilled the call of the Prophet (pbuh) and confirmed it. They were six and all of the Khazrajs. When the Khazraj returned to their territory, Islam spread in Medina. So that there is not a single house belonging to the Ansar but in it is mentioned the Prophet Muhammad SAW.