To retrieve all artifacts containing a SHA1 file hash via the Splunk SOAR REST API, the appropriate query would filter for artifacts where the 'cef_sha1' field is not null, indicating that a SHA1 hash is present. The correct REST API call should use the filter parameter _filter_cef_shal__isnull=False (assuming 'shal' is a typo and it should be 'sha1'). This query parameter is used to filter out artifacts that do not have a SHA1 hash, thus returning only those that do.