The Muslims in Makkah faced open persecution, threats and torture. In Rajab of the 5th year of the mission, the Prophet ﷺ said to his Companions, "This land has become too constricted for you, so for those of you who want to, why don't you emigrate to the neighboring land of Abyssinia? For there is a Christian king there, who is a just king. He shall allow you to worship without interference." That king was the Najashi (Negus) of Abyssinia, As'hama ibn Abjar.
Fifteen people emigrated, 11 men and 4 women. They travelled for about a day and a half to the port of Juddah (today's Jeddah), and from there took a ship to Abyssinia. Among them were Uthman ibn Affan and his wife Ruqayyah, the Prophet ﷺ's daughter. Others included Abd al-Rahman ibn Awf, Uthman ibn Maz'un, Zubayr ibn al-Awwam and Mus'ab ibn Umayr. Abu Salama went with his wife Umm Salama, and Amir ibn Rabi'ah with his wife Layla.
All of those who went were Muslims of high standing in the Quraysh, who had the freedom to leave. The lower-status believers, many of them slaves, could not go, even though they needed it most. These included Bilal, Khabbab, Ibn Mas'ud and Ammar.