Umm al-Mu'minin Sayyidah Umm Salamah (may Allah be pleased with her) said: When Makkah became constricted for us, and the Companions of the Messenger of Allah (peace and blessings be upon him) faced all kinds of hardships and afflictions, and they saw trials and persecution because of (practising) their religion, and (they saw) that the Messenger of Allah (peace and blessings be upon him) was unable to ward this off from them, while the Messenger of Allah (peace and blessings be upon him) himself was under the protection of his people and his uncle, so that none of the harm that befell his companions reached him, he (peace and blessings be upon him) said to them: "In the land of Abyssinia there is a king with whom no one is wronged, so go to his country, until Allah Almighty makes some other way out for you (from what you are in)." Then we left gradually (in groups), until we all gathered in Abyssinia, and we were in a good home and with a good neighbour, and there was no fear of injustice or oppression there. Then she narrated the long hadith.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 17734