The first immigration to Abyssinia was in the month of Rajab in the 5th year of the call. Um Salamah (may Allah be pleased with her) told us the reason for this first immigration to Abyssinia, saying, «The difficulties in Mecca increased, the Prophet’s Companions were harmed, and the trials and tests they suffered made it difficult for them to practice their religion. Moreover, the Prophet (peace be upon him) was unable to protect them from such harm although he himself was protected by his tribe and uncle. Consequently, he did not suffer any of the harm that his Companions suffered. For these reasons, he told his Companions, ‘In Abyssinia, there is a king who does not oppress anyone in his land, so go to his country and stay there until Allah gives you a way out of your difficulties’»[related by Al-Bayhaqi in Sunan Al-Kubra].
The first immigrants to Abyssinia were Uthman ibn Affan and his wife Ruqayah, daughter of the Prophet, Abu Hatheefah ibn Utbah ibn Rabi’ah and his wife Sahla bint Sahayl ibn Amr, Az-Zubair ibn Al-Awwam ibn Asad, Musab ibn Umair ibn Hashim ibn Abd-Manaf ibn Abdul-Dar, Abdur-Rahman ibn Awf ibn Abdu Awf ibn Abd ibn Al-Harith ibn Zahrah, Abu Salama ibn Abdul-Asad ibn Halal ibn Abdullah ibn Makhzum and his wife Um Salama bint Abu Umayya ibn Al-Mughirah, Uthman ibn Mazun Al-Jumahi, Amer ibn Rabi’ah Al-Anzy supporter of Bani Adi ibn Kaab and his wife Leila bint Abu Hathamah, Abu Sabra ibn Abu Raham ibn Abdul-Uzza Al-Amari, Hatib ibn Umar ibn Abdush-Shams, Suhayl ibn Bayda from Bani Al-Harith ibn Fehr, and Abdullah ibn Masoud supporter of Bani Zahrah [At-Tabaqat Al-Kobra, The History of Al-Tabari].
These twelve men and four women left Mecca and reached the coast of the Red Sea. Uthman ibn Mazun was assigned as their leader [The Prophet’s Biography by Ibn Hesham]. At the Red Sea they found two ships, so they boarded them for half a dinar each. At that time, Quraysh realized that the Companions (may Allah be pleased with them) had left and as a result they quickly went to the coast to follow them, but the Companions had already left the harbour. That was in the month of Rajab in the fifth year of the call [The Beginning and the End, volume 3].
When Abu Bakr (may Allah be pleased with him) wanted to immigrate to Abyssinia after Quraysh started to harm him more, he took the journey to Yemen. When he reached Barak Al-Ghamad, he met Ibn Ad-Daghunah, who was the master of the tribes there and a supporter of Bani Zahra Al-Qarashiyah. He asked Abu Bakr, "Where are you going, Abu Bakr?" Abu Bakr replied, "My people have pushed me out of my city, so I want to wander throughout the land worshipping Allah." Ibn Ad-Daghunah said, "One like you should not leave his city or be exiled from it, as you assume others’ responsibilities by spending on the weak, orphans and needy who cannot look after themselves, keep good relations with your relatives, do more good than anyone else, are hospitable to your guests, and help those afflicted by calamities." Consequently, he offered him protection and returned with him to Mecca, where he announced to Quraysh that Abu Bakr was under his protection. Quraysh accepted this protection of Abu Bakr from Ibn Ad-Daghunah, but they laid down the condition that Abu Bakr should only worship Allah in his house, and not outside in front of others. Abu Bakr used to pray in the courtyard of his house (and he used to cry there, being unable to control his tears, when he read the Quran) and as a result the people used to gather around him and listen to him reading the Quran, which annoyed Quraysh. Even Ibn Ad-Daghunah asked Abu Bakr to not worship Allah in the open, threatening that he would stop giving him protection if he did. But Abu Bakr (may Allah be pleased with him) agreed to go without his protection to be able to worship Allah in front of others, saying "I am forgoing your protection to be satisfied with Allah’s protection instead." Abu Bakr stayed in Mecca with the possibility of his people harming him, although the Prophet (peace be upon him) gave him permission to immigrate to Abyssinia [The Prophet’s Biography by Ibn Hesham and Fat-h Al-Bari].
But the Companions (may Allah be pleased with them) did not stay in Abyssinia for long this time, as when the Prophet (peace be upon him) read Surah An-Najm in front of the polytheists of Mecca and he reached the ayah of prostration, he prostrated and the Muslims, polytheists and even the jinn prostrated with him; all of the people prostrated [related by Al-Bukhari].
The news of the Meccan polytheists prostrating reached those who had immigrated to Abyssinia, giving them the idea that the polytheists had embraced Islam. Consequently, a group of them returned towards Mecca, but the others stayed in Abyssinia. One group intended well, but the other group took the correct decision. However, when they came near Mecca and realized that what they had heard about the people of Mecca was false, they all entered Mecca either surreptitiously or under the protection of one of the members of Quraysh.