Sahih Bukhari
Merits of the Helpers in Madinah (Ansaar)
Volume: 005 / Book Number: 058 / Hadith Number: 261
Narrated Al-Bara:
The first people who came to us (in Medina) were Mus'ab bin 'Umar and Ibn Um Maktum. Then came to us 'Ammar bin Yasir and Bilal.