Complex sentence: Jabir ibn Abdullah al-Ansari was born in Medina (then known Yathrub) 15 years before the hijra--he belonged to a poor family of Yathrub.
Split into simpler sentences: Jabir ibn Abdullah al-Ansari was born in Medina (then known Yathrub) 15 years before the Hijra. He belonged to a poor family of Yathrub.