So start with 8.4.1.1 which requires the definition of externally provided products, processes, and services to include sorting, among others.
8.4.2.3 requires those suppliers to develop, implement and improve a QMS certified to ISO, unless otherwise authorized by the customer, with the ultimate objective of becoming IATF certified. It then lists several steps, such as min. Automotive supplier criteria, compliance wit IATF, etc.
So in response to Hender's question, their sorting suppliers should be ISO or at least working toward it and eventually toward IATF.