When referring to more than one source when a statement is made, arrange the references alphabetically according to the first author, in the same order, they will appear in the reference list. Use a semi-colon after each reference.
If you use the Harvard referencing style click here https://libguides.nwu.ac.za/harvard-referencing/text-references (see tab Text references to more than one source) for more info.
If you use the APA referencing style click here https://libguides.nwu.ac.za/apa-referencing/ebooks (see tab Text references to more than one source) for more info.