it was recorded by al-Nasāʾī (8403), al-Ḥākim (3/437), Ibn Abī Shaybah (14/462/1875), Ibn Abī ʿĀṣim in "al-Sunnah" (2/608), and al-Bazzār in "Musnad" (2/338/1814) through various chains from ʿAwf from him; Ibn Abī Shaybah and al-Bazzār added; and they only mentioned the dispatch of ʿUmar: "He met the people of Khaybar, and they repelled him and exposed him and his companions, so they returned to the Messenger of Allāh (ṣallá Allāhu ʿalayhi wa-sallam) while he was discouraging his companions, and his companions were discouraging him." Perhaps this is among the rejected narrations of this Maimūn, who was the freedman of ʿAbd al-Raḥmān ibn Samurah, as there is consensus on his weakness, contrary to Ibn Ḥibbān who mentioned him in "al-Thiqāt" (5/418), yet he also said: "Yaḥyá al-Qaṭṭān had a poor opinion of him." al-Dhahabī mentioned him in "al-Mughnī," and said: "Aḥmad said: His ḥadīths are rejected." He was also followed by al-Musayyib ibn Muslim al-Azdī who said: ʿAbd Allāh ibn Buraydah narrated it to us, and it includes the mention of the two ʿUmars and their intense fighting without victory, but it includes the phrase (discouragement). al-Ḥākim recorded it (3/37) in a summarized form, and al-Bayhaqī in its entirety (4/210-212), and al-Ḥākim said: "Its isnād is authentic." al-Dhahabī agreed with him! I say: I did not find a biography for this al-Musayyib in the sources I have, nor did al-Mizzī mention him among the narrators from ʿAbd Allāh ibn Buraydah, nor among the teachers of Yūnus ibn Bukayr who narrates from him here, so it appears he is unknown. And Allāh knows best