“…If they find fault with his command, they have already found fault with his father’s command. By Allah, he was indeed fit for leadership, and he was among the people I loved most. And this son of his is, after him, among the people I love most.” (1)
I add: When the Prophet ﷺ put him in charge of that army, he was eighteen years old.
Ibn Saʿd reports: Yazīd narrated to us; Ḥammād ibn Salamah narrated to us, from Hishām ibn ʿUrwah, from his father:
The Prophet ﷺ postponed the departure from ʿArafah because of Usāmah, waiting for him. A black youth with a flat nose then appeared, and the people of Yemen exclaimed, “Is it for this one that we have been kept sitting?!”
Because of that they later apostatized—meaning during the Days of Apostasy. (2)
Wakīʿ said: Among the well-known Companions who were spared the turmoil were Saʿd, Ibn ʿUmar, Usāmah ibn Zayd, and Muḥammad ibn Maslamah.
I say: Usāmah profited from that day of the Prophet ﷺ when he would say to him, “How (3) lā ilāha illā…”
(1) Reported by al-Bukhari, 7/69 (Book of Virtues, chapter: The Merits of Zayd), 3/382 (Book of Military Expeditions, chapter: The Expedition of Zayd ibn Haritha), 8/115 (same book), and 11/455 (Book of Faith and Vows); by Muslim, no. 2426, sections 63–64; by Ibn Saʿd, 4/65; by Ahmad, 2/20; and by al-Tirmidhi, no. 3816.
(2) All the transmitters in its chain are reliable. The narrator Yazid is Yazid ibn Harun. The report is also found in Ibn Saʿd, Tabaqat, 4/63, and in al-Bukhari’s al-Tarikh al-Kabir, 2/20, through the isnad of ʿAyash ibn ʿAbbas → ʿIsa ibn Musa → Muhammad ibn Iyas al-Kabir → Usama ibn Zayd.
(3) The printed edition has the mistaken reading “kaf.” The hadith is recorded by Muslim, no. 97 (Book of Faith, chapter: The prohibition of killing a non-Muslim after he has said la ilaha illa Allah). It recounts that Usama ibn Zayd killed a man from the polytheists after the latter had pronounced la ilaha illa Allah, whereupon the Prophet ﷺ asked: “Why did you kill him?” Usama replied: “Messenger of Allah, he had injured the Muslims and killed so-and-so,” naming several men. “I attacked him, and when he saw the sword he said la ilaha illa Allah.” The Prophet repeated: “Did you kill him?” Usama said yes. The Prophet then asked: “How will you answer for la ilaha illa Allah when it comes on the Day of Resurrection?” Usama pleaded: “Messenger of Allah, ask forgiveness for me….” See also al-Bukhari, 7/398 (Book of Military Expeditions, chapter: The Prophet’s dispatch of Usama ibn Zayd against the Hurqat clan of Juhayna) and Muslim, no. 96.