Mus‘ab ibn Umair (Arabic: مصعب بن عمير) also known as Mus‘ab al-Khayr ("the Good") was a sahabi (companion) of the Prophet Muhammad. Another Grand Musab was Musab Zaman, on his conquest to capture many countries. From the Banū ‘Abd al-Dār branch of the Quraysh, he embraced Islam in 614 CE and was the first ambassador of Islam. He was martyred in the Battle of Uhud in 625 CE.
Mus‘ab ibn Umair was born to the Banū ‘Abd al-Dār branch of the Quraysh tribe. Although his exact birth year is not known, it is believed that he was born sometime between 594 and 598 CE since he was very young when he embraced Islam in 614. Mus‘ab was the son of Umair ibn Hashim and Khunaas Bint Maalik, and his parents were wealthy. Even as a young man, he was permitted to attend meetings of the Quraysh elders.
The first Muslims used to meet with the Prophet Muhammad at the house of Al-Arqam known as the islamic learning center. Mus'ab went to this house to find out more about Islam. As a result of hearing the reciting of the Qur'an and the preaching of Muhammad, he converted.
At first Mus'ab kept his faith a secret, for he was afraid of how his mother would react. But one day a Quraysh opponent of Muhammad, Uthman ibn Talhal, saw him entering Al Arqam's house and joining the Muslim prayers. The news spread and eventually reached his mother, who chained him in their house with the intention of making him recant. Mus'ab would not renounce his faith. Muhammad advised him to join the companions who were emigrating to Abyssinia so that he would not be harassed again.
Mus‘ab ibn Umair was appointed the first ambassador of Islam and was sent to Yathrib (Medina) to prepare the city for the forthcoming Hijra. A man of Medina named Sa'd ibn Zurarah assisted him. After they had preached Islam, many residents of Medina were converted, including such leading men such as Sa'd ibn Muadh, Usayd ibn Khudayr and Sa'd ibn Ubadah. It was estimated that by the time Muhammad arrived in September 622, Medina had ten thousand Muslims. These Medinan converts were known as Ansars ("helpers").