When it became difficult for the Muslims of Mecca to bear the persecutions of Quraish, then our holy prophet Muhammad (Peace be upon him) allowed them to move to Abyssinia where the King was from the Christian religion. The king of Abyssinia was known as Nijashi (Negus). In the 5th year of prophet-hood, 16 people including 4 women migrated to Abyssinia. The third caliph, Hazrat Usman was also included in these 16 people along with his wife, Ruqayya, who was the daughter of our holy prophet Muhammad (Peace be upon him).
After some time, they heard the news that now the behavior of Quraish has been changed now and they are now friendly with the Muslims and many of them have been accepted Islam as well. They decided to come back to Mecca. When they came near to Mecca, they knew that this news was not more than a rumor. They went back to Abyssinia. Later on, our holy prophet Muhammad (Peace be upon him) allowed some other people to go to Abyssinia. This time the total number of Muslims reached about 101 including 18 women and children.
This migration made the Quraish afraid of the Muslims as they had trade relations with Abyssinia. If Muslims spread Islam over there in the Abyssinia, their relations with Abyssinia may come endanger. They sent a deputation under the leadership of Amr bin Al-Aas to Nijashi to get these Muslims back. Amr bin Al-Aas presented gifts to Nijashi and informed him that they are Muslims and they have left our religion which is different from your religion as well so return these people back to us. Then Nijashi asked the Muslims about their religion. Hazrat Jaffar Tayyar represented the teachings of Islam in front of Nijashi. He said that we were ignorant, corrupt and cruel to each other. Then our Prophet Muhammad (Peace be upon him) informed about only one God, ALLAH. He told us about right and wrong, legal and illegal and taught us about equality between rich and poor. Then Nijashi asked him about to recite some of the Ayaat from the Holy Quran. Then Hazrat Jaffar Tayyar recited some ayat from Surah Maryam where Hazrat Isa was discussed. After listening to this ayat, Nijashi refused to return the Muslims and returned back the gifts of Quraish.
The main reason behind the migration to Abyssinia was the persecution of the Quraish. When these persecutions became unbearable, our holy prophet Muhammad (Peace be upon him) allowed Muslims to migrate to Abyssinia as the King of the Abyssinia was kind-hearted and their religion was close to the Islam. It was possible for Muslims to practice Islam freely over there in Abyssinia. They could live there free from the persecutions of Quraish. Most of the Muslims joined our holy prophet Muhammad (Peace e upon him) after the migration to Medina while the rest of them called to join the Muslims in 7th Hijri.