How does “khabarayn” function in the Abū ʿAmr and Abū Maʿmar sentence?

Historical Examples of Muʿanʿan Transmission and the Conclusion of Muslim’s Introduction

• Each transmitted two reports from Abū Masʿūd
• They transmitted only one report each jointly
• Only Abū ʿAmr transmitted two; Abū Maʿmar transmitted one
• Two reports omit the Companion intermediary