Madinah (Yathrib) was populated with many tribes, but most prominent were the tribes of Aus and Khazraj. There were also a separate section of Madinah which was dominated by the Jews.
The tribes of Khazraj was foremost in the quest for Islam and, very soon, Islam was growing roots among some of the tribes of Arabia.
As the thirteenth year of Nubuwwat drew to a close seventy Muslims, including two women, came to Makkah to perform pilgrimage and to meet Rasulullah at Aqabah. This deputation of Muslims was led by Hazrat Mus'ab-bin-Umayr (R.A.) and they were specifically sent by the Muslims of Madinah to request Rasulullah to migrate with them to Madinah.
Accompanied by Hazrat Abbas (R.A.), who had not as yet embraced Islam, Rasulullah left Makkah at night to meet the deputation. Hazrat Mus'ab-bin-Umayr (R.A.) was very cautious and thought it necessary to remind them that Rasulullah was protected by the Hashimites in Makkah. The Muslims of Madinah would have to sacrifice their lives and face bloody wars for his protection. If they were prepared for the consequences then only should they ask Rasulullah to leave Makkah.
Rasulullah also stressed the serious risk they would be taking and the responsibilities that would confront the Muslims of Madinah.
The determined Muslims pledged on the hand of Rasulullah that they will sacrifice their lives to protect him and Islam, as they would their wives and children. This was the Second Covenant of Aqabah.
Rasulullah chose twelve Muslims of Madinah for the propagation of Islam of whom nine were from the tribes of Khazraj. After the pledge had been taken, Rasulullah decided to migrate to Madinah. His first thought was for all the Muslims of Makkah and their safety. He gave general directive to the Muslims to migrate. However, the Quraish devised tragic obstacles in the path of the Muslims, which resulted in heart-breaks, separations, beatings, the seizing of properties and personal belongings. Ultimately, there were only a few Muslims left in Makkah and Rasulullah awaited the Divine guidance for his departure for Madinah.
Contents of the biography of the Prophet Muhammed