Saya mau tau Latar Belakang dari Abdallah ibn Yasin. Jelaskan dalam bahasa melayu

Norris, H.T. 1971. New evidence on the life of ‘Abdullah B. Yasin and the origins of the Almoravid movement. The Journal of African History, Vol. 12, No. 2 (1971), pp. 255–268.