Musnad Ahmad 788:208

Abu Abd al-Rahman Abdullah ibn Yazid narrated to us, al-Mas'udi narrated to us, from Adi ibn Thabit, from Abu Burdah, from Abu Musa, who said: Umar met Asma bint Umays, may Allah be pleased with them both, and said: "What an excellent people you are! Were it not that you preceded us in the migration (Hijrah), we would be better than you." She said: "You were with the Messenger of Allah, may Allah bless him and grant him peace; he would teach your ignorant ones and feed your hungry ones, while we fled with our religion." She said: "I will not rest until I enter upon the Messenger of Allah, may Allah bless him and grant him peace." So she entered and mentioned what Umar, may Allah be pleased with him, had said to her. The Messenger of Allah, may Allah bless him and grant him peace, said: "Rather, you have two migrations: your migration to Abyssinia and your migration to Medina."