Prior to the major British overhaul of Perak's administration, slavery was widely practised along with a type of corvée labour system, called "kerah". The chief of a given area could call on his citizens to work as forced labour without pay, although under normal circumstances food was still provided. The system was created to ensure the maintenance of the ruling class. It was often described as onerous and demanding, as there were times when the call to duty, and its duration, interfered with citizens' individual work. The slaves were divided into two classes: debtor-bondsmen and ordinary slaves. The debtor-bondsmen had the higher status, being ranked as free men and acknowledged as members of their masters' society. In contrast, the ordinary slaves had no prospect of status redemption. As Islam does not allow enslavement of fellow Muslims, the ordinary slaves came mainly from non-Muslim groups, especially the Orang Asli, Batak, and Africans purchased by Malays on pilgrimage in Mecca.