To what extent are the two sermons attributed to Umar ibn al-Khattab, may Allah be pleased with him, authentic: one that speaks of Salman al-Farisi's questioning Umar about the source of his garment, and the other about the story of Jabalah ibn al-Ayham when he slapped the black slave during the Hajj season?

As for the first story, it is mentioned in history books without a chain of narration (isnad (definition)). Some, like Ibn Qutaybah and Ibn al-Jawzi, attributed it to Al-Utbi, who is Muhammad ibn Ubayd Allah al-Umawi. Al-Dhahabi said about him in Siyar A'lam al-Nubala': "He used to drink, and he had literary works and fame." There are vast distances between his era and the era of the Companions. The meaning of this story contains a denunciation, and it is among what Imam Ahmad's saying applies to: "Three sciences have no origin: tafsir (definition) (exegesis), history, and malāhim (apocalyptic prophecies)."

As for the second story, it is very famous, and historians and biographers mention it as an established fact. However, it does not have a sound chain of narration; rather, it is either un-narrated or from the narration of weak and abandoned narrators like Al-Waqidi, with variations in its context between one narration and another. The famous version is what Ibn Sa'd mentioned in Al-Tabaqat al-Kubra regarding the conversion of Jabalah ibn al-Ayham to Islam by a letter from the Messenger of Allah, peace be upon him, and then his apostasy during the time of Umar ibn al-Khattab after a man from Muzaynah slapped him, and his refusal to accept retribution. This was difficult for Umar. Al-Waqidi narrated it from Ma'mar and others from Al-Zuhri from Ubayd Allah ibn Abdullah from Ibn Abbas. It should be noted that Jabalah's conversion to Islam itself is a matter of dispute among historians; some affirmed his conversion and then his apostasy, while others said that he never embraced Islam at all. And Allah knows best.